[edk2-devel] [PATCH 1/1] OvmfPkg/ResetVector: send post codes to qemu debug console

[edk2-devel] [PATCH 1/1] OvmfPkg/ResetVector: send post codes to qemu debug console

[Gerd Hoffmann]

Neat when doing ResetVector coding.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 OvmfPkg/ResetVector/DebugCon.asm      | 43 +++++++++++++++++++++++++++
 OvmfPkg/ResetVector/ResetVector.nasmb |  2 +-
 2 files changed, 44 insertions(+), 1 deletion(-)
 create mode 100644 OvmfPkg/ResetVector/DebugCon.asm

diff --git a/OvmfPkg/ResetVector/DebugCon.asm b/OvmfPkg/ResetVector/DebugCon.asm
new file mode 100644
index 000000000000..9c57d1a52c75
--- /dev/null
+++ b/OvmfPkg/ResetVector/DebugCon.asm
@@ -0,0 +1,43 @@
+;------------------------------------------------------------------------------
+; @file
+; qemu debug console support macros (based on serial port macros)
+;
+; Copyright (c) 2008 - 2018, Intel Corporation. All rights reserved.<BR>
+; SPDX-License-Identifier: BSD-2-Clause-Patent
+;
+;------------------------------------------------------------------------------
+
+%macro  outToDebugPort 1
+    mov     dx, 0x402
+    mov     al, %1
+    out     dx, al
+%endmacro
+
+%macro  debugShowCharacter 1
+    outToDebugPort %1
+%endmacro
+
+%macro  debugShowHexDigit 1
+  %if (%1 < 0xa)
+    debugShowCharacter BYTE ('0' + (%1))
+  %else
+    debugShowCharacter BYTE ('a' + ((%1) - 0xa))
+  %endif
+%endmacro
+
+%macro  debugNewline 0
+    debugShowCharacter `\r`
+    debugShowCharacter `\n`
+%endmacro
+
+%macro  debugShowPostCode 1
+    debugShowHexDigit (((%1) >> 4) & 0xf)
+    debugShowHexDigit ((%1) & 0xf)
+    debugNewline
+%endmacro
+
+BITS    16
+
+%macro  debugInitialize 0
+    ; not required
+%endmacro
diff --git a/OvmfPkg/ResetVector/ResetVector.nasmb b/OvmfPkg/ResetVector/ResetVector.nasmb
index 5832aaa8abf7..f1655ddfcde3 100644
--- a/OvmfPkg/ResetVector/ResetVector.nasmb
+++ b/OvmfPkg/ResetVector/ResetVector.nasmb
@@ -41,7 +41,7 @@
 %elifdef DEBUG_SERIAL
   %include "SerialDebug.asm"
 %else
-  %include "DebugDisabled.asm"
+  %include "DebugCon.asm"
 %endif
 
 %include "Ia32/SearchForBfvBase.asm"
-- 
2.43.0



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Re: [edk2-devel] [PATCH 1/1] OvmfPkg/ResetVector: send post codes to qemu debug console

[Laszlo Ersek]

On 1/24/24 16:31, Gerd Hoffmann wrote:
> Neat when doing ResetVector coding.
> 
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  OvmfPkg/ResetVector/DebugCon.asm      | 43 +++++++++++++++++++++++++++
>  OvmfPkg/ResetVector/ResetVector.nasmb |  2 +-
>  2 files changed, 44 insertions(+), 1 deletion(-)
>  create mode 100644 OvmfPkg/ResetVector/DebugCon.asm
> 
> diff --git a/OvmfPkg/ResetVector/DebugCon.asm b/OvmfPkg/ResetVector/DebugCon.asm
> new file mode 100644
> index 000000000000..9c57d1a52c75
> --- /dev/null
> +++ b/OvmfPkg/ResetVector/DebugCon.asm
> @@ -0,0 +1,43 @@
> +;------------------------------------------------------------------------------
> +; @file
> +; qemu debug console support macros (based on serial port macros)
> +;
> +; Copyright (c) 2008 - 2018, Intel Corporation. All rights reserved.<BR>
> +; SPDX-License-Identifier: BSD-2-Clause-Patent
> +;
> +;------------------------------------------------------------------------------
> +
> +%macro  outToDebugPort 1
> +    mov     dx, 0x402
> +    mov     al, %1
> +    out     dx, al
> +%endmacro
> +
> +%macro  debugShowCharacter 1
> +    outToDebugPort %1
> +%endmacro
> +
> +%macro  debugShowHexDigit 1
> +  %if (%1 < 0xa)
> +    debugShowCharacter BYTE ('0' + (%1))
> +  %else
> +    debugShowCharacter BYTE ('a' + ((%1) - 0xa))
> +  %endif
> +%endmacro
> +
> +%macro  debugNewline 0
> +    debugShowCharacter `\r`
> +    debugShowCharacter `\n`
> +%endmacro
> +
> +%macro  debugShowPostCode 1
> +    debugShowHexDigit (((%1) >> 4) & 0xf)
> +    debugShowHexDigit ((%1) & 0xf)
> +    debugNewline
> +%endmacro
> +
> +BITS    16
> +
> +%macro  debugInitialize 0
> +    ; not required
> +%endmacro
> diff --git a/OvmfPkg/ResetVector/ResetVector.nasmb b/OvmfPkg/ResetVector/ResetVector.nasmb
> index 5832aaa8abf7..f1655ddfcde3 100644
> --- a/OvmfPkg/ResetVector/ResetVector.nasmb
> +++ b/OvmfPkg/ResetVector/ResetVector.nasmb
> @@ -41,7 +41,7 @@
>  %elifdef DEBUG_SERIAL
>    %include "SerialDebug.asm"
>  %else
> -  %include "DebugDisabled.asm"
> +  %include "DebugCon.asm"
>  %endif
>  
>  %include "Ia32/SearchForBfvBase.asm"

(1) How much output does this produce? Trapping to QEMU for every single
character written to the debug console is very slow. If it only produces
a few bytes, that should be OK.

(2) debugInitialize could actually be put to use; the presence of the
QEMU debug console is detectable. We'd need to allocate a single byte
somewhere, detect the console in debugInitialize, save the result in
that byte, then check the byte in debugShowPostCode. Eliminates even
those few (?) traps if there is no debug console configured.

(3) I'm already hating myself for asking about this, but... is there a
way for only customizing debugInitialize and debugShowCharacter? The
rest is common with "SerialDebug.asm", and I wish I hadn't had to review
those (unchanged) macros, they make my eyes bleed :/

Anyway, if you think any of these (or all of these!) means too much
work, I'm OK with the patch going-in as is.

I'm a bit concerned about (1), TBH.

Laszlo



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Re: [edk2-devel] [PATCH 1/1] OvmfPkg/ResetVector: send post codes to qemu debug console

[Lendacky, Thomas via groups.io]

On 1/24/24 10:47, Laszlo Ersek wrote:
> On 1/24/24 16:31, Gerd Hoffmann wrote:
>> Neat when doing ResetVector coding.
>>
>> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
>> ---
>>   OvmfPkg/ResetVector/DebugCon.asm      | 43 +++++++++++++++++++++++++++
>>   OvmfPkg/ResetVector/ResetVector.nasmb |  2 +-
>>   2 files changed, 44 insertions(+), 1 deletion(-)
>>   create mode 100644 OvmfPkg/ResetVector/DebugCon.asm
>>
>> diff --git a/OvmfPkg/ResetVector/DebugCon.asm b/OvmfPkg/ResetVector/DebugCon.asm
>> new file mode 100644
>> index 000000000000..9c57d1a52c75
>> --- /dev/null
>> +++ b/OvmfPkg/ResetVector/DebugCon.asm
>> @@ -0,0 +1,43 @@
>> +;------------------------------------------------------------------------------
>> +; @file
>> +; qemu debug console support macros (based on serial port macros)
>> +;
>> +; Copyright (c) 2008 - 2018, Intel Corporation. All rights reserved.<BR>
>> +; SPDX-License-Identifier: BSD-2-Clause-Patent
>> +;
>> +;------------------------------------------------------------------------------
>> +
>> +%macro  outToDebugPort 1
>> +    mov     dx, 0x402
>> +    mov     al, %1
>> +    out     dx, al
>> +%endmacro
>> +
>> +%macro  debugShowCharacter 1
>> +    outToDebugPort %1
>> +%endmacro
>> +
>> +%macro  debugShowHexDigit 1
>> +  %if (%1 < 0xa)
>> +    debugShowCharacter BYTE ('0' + (%1))
>> +  %else
>> +    debugShowCharacter BYTE ('a' + ((%1) - 0xa))
>> +  %endif
>> +%endmacro
>> +
>> +%macro  debugNewline 0
>> +    debugShowCharacter `\r`
>> +    debugShowCharacter `\n`
>> +%endmacro
>> +
>> +%macro  debugShowPostCode 1
>> +    debugShowHexDigit (((%1) >> 4) & 0xf)
>> +    debugShowHexDigit ((%1) & 0xf)
>> +    debugNewline
>> +%endmacro
>> +
>> +BITS    16
>> +
>> +%macro  debugInitialize 0
>> +    ; not required
>> +%endmacro
>> diff --git a/OvmfPkg/ResetVector/ResetVector.nasmb b/OvmfPkg/ResetVector/ResetVector.nasmb
>> index 5832aaa8abf7..f1655ddfcde3 100644
>> --- a/OvmfPkg/ResetVector/ResetVector.nasmb
>> +++ b/OvmfPkg/ResetVector/ResetVector.nasmb
>> @@ -41,7 +41,7 @@
>>   %elifdef DEBUG_SERIAL
>>     %include "SerialDebug.asm"
>>   %else
>> -  %include "DebugDisabled.asm"
>> +  %include "DebugCon.asm"
>>   %endif
>>   
>>   %include "Ia32/SearchForBfvBase.asm"
> 
> (1) How much output does this produce? Trapping to QEMU for every single
> character written to the debug console is very slow. If it only produces
> a few bytes, that should be OK.
> 
> (2) debugInitialize could actually be put to use; the presence of the
> QEMU debug console is detectable. We'd need to allocate a single byte
> somewhere, detect the console in debugInitialize, save the result in
> that byte, then check the byte in debugShowPostCode. Eliminates even
> those few (?) traps if there is no debug console configured.
> 
> (3) I'm already hating myself for asking about this, but... is there a
> way for only customizing debugInitialize and debugShowCharacter? The
> rest is common with "SerialDebug.asm", and I wish I hadn't had to review
> those (unchanged) macros, they make my eyes bleed :/
> 
> Anyway, if you think any of these (or all of these!) means too much
> work, I'm OK with the patch going-in as is.

My concern would be around SEV-ES/SEV-SNP guest usage. The in and out 
instruction will generate a #VC and would require a #VC handler to be in 
place.

I'm pretty sure this will cause issues for those types of guests, but it 
might be a few days before I can get to it to verify. @Gerd, were you able 
to test this with those types of guests?

Thanks,
Tom

> 
> I'm a bit concerned about (1), TBH.
> 
> Laszlo
> 


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Re: [edk2-devel] [PATCH 1/1] OvmfPkg/ResetVector: send post codes to qemu debug console

[Lendacky, Thomas via groups.io]

On 1/24/24 13:24, Tom Lendacky wrote:
> On 1/24/24 10:47, Laszlo Ersek wrote:
>> On 1/24/24 16:31, Gerd Hoffmann wrote:
>>> Neat when doing ResetVector coding.
>>>
>>> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
>>> ---
>>>   OvmfPkg/ResetVector/DebugCon.asm      | 43 +++++++++++++++++++++++++++
>>>   OvmfPkg/ResetVector/ResetVector.nasmb |  2 +-
>>>   2 files changed, 44 insertions(+), 1 deletion(-)
>>>   create mode 100644 OvmfPkg/ResetVector/DebugCon.asm
>>>
>>> diff --git a/OvmfPkg/ResetVector/DebugCon.asm 
>>> b/OvmfPkg/ResetVector/DebugCon.asm
>>> new file mode 100644
>>> index 000000000000..9c57d1a52c75
>>> --- /dev/null
>>> +++ b/OvmfPkg/ResetVector/DebugCon.asm
>>> @@ -0,0 +1,43 @@
>>> +;------------------------------------------------------------------------------
>>> +; @file
>>> +; qemu debug console support macros (based on serial port macros)
>>> +;
>>> +; Copyright (c) 2008 - 2018, Intel Corporation. All rights reserved.<BR>
>>> +; SPDX-License-Identifier: BSD-2-Clause-Patent
>>> +;
>>> +;------------------------------------------------------------------------------
>>> +
>>> +%macro  outToDebugPort 1
>>> +    mov     dx, 0x402
>>> +    mov     al, %1
>>> +    out     dx, al
>>> +%endmacro
>>> +
>>> +%macro  debugShowCharacter 1
>>> +    outToDebugPort %1
>>> +%endmacro
>>> +
>>> +%macro  debugShowHexDigit 1
>>> +  %if (%1 < 0xa)
>>> +    debugShowCharacter BYTE ('0' + (%1))
>>> +  %else
>>> +    debugShowCharacter BYTE ('a' + ((%1) - 0xa))
>>> +  %endif
>>> +%endmacro
>>> +
>>> +%macro  debugNewline 0
>>> +    debugShowCharacter `\r`
>>> +    debugShowCharacter `\n`
>>> +%endmacro
>>> +
>>> +%macro  debugShowPostCode 1
>>> +    debugShowHexDigit (((%1) >> 4) & 0xf)
>>> +    debugShowHexDigit ((%1) & 0xf)
>>> +    debugNewline
>>> +%endmacro
>>> +
>>> +BITS    16
>>> +
>>> +%macro  debugInitialize 0
>>> +    ; not required
>>> +%endmacro
>>> diff --git a/OvmfPkg/ResetVector/ResetVector.nasmb 
>>> b/OvmfPkg/ResetVector/ResetVector.nasmb
>>> index 5832aaa8abf7..f1655ddfcde3 100644
>>> --- a/OvmfPkg/ResetVector/ResetVector.nasmb
>>> +++ b/OvmfPkg/ResetVector/ResetVector.nasmb
>>> @@ -41,7 +41,7 @@
>>>   %elifdef DEBUG_SERIAL
>>>     %include "SerialDebug.asm"
>>>   %else
>>> -  %include "DebugDisabled.asm"
>>> +  %include "DebugCon.asm"
>>>   %endif
>>>   %include "Ia32/SearchForBfvBase.asm"
>>
>> (1) How much output does this produce? Trapping to QEMU for every single
>> character written to the debug console is very slow. If it only produces
>> a few bytes, that should be OK.
>>
>> (2) debugInitialize could actually be put to use; the presence of the
>> QEMU debug console is detectable. We'd need to allocate a single byte
>> somewhere, detect the console in debugInitialize, save the result in
>> that byte, then check the byte in debugShowPostCode. Eliminates even
>> those few (?) traps if there is no debug console configured.
>>
>> (3) I'm already hating myself for asking about this, but... is there a
>> way for only customizing debugInitialize and debugShowCharacter? The
>> rest is common with "SerialDebug.asm", and I wish I hadn't had to review
>> those (unchanged) macros, they make my eyes bleed :/
>>
>> Anyway, if you think any of these (or all of these!) means too much
>> work, I'm OK with the patch going-in as is.
> 
> My concern would be around SEV-ES/SEV-SNP guest usage. The in and out 
> instruction will generate a #VC and would require a #VC handler to be in 
> place.
> 
> I'm pretty sure this will cause issues for those types of guests, but it 
> might be a few days before I can get to it to verify. @Gerd, were you able 
> to test this with those types of guests?

Had a meeting get canceled and so got a chance to test this. As I thought, 
this causes SEV-ES/SEV-SNP guest failures.

Thanks,
Tom

> 
> Thanks,
> Tom
> 
>>
>> I'm a bit concerned about (1), TBH.
>>
>> Laszlo
>>


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Re: [edk2-devel] [PATCH 1/1] OvmfPkg/ResetVector: send post codes to qemu debug console

[Erdem Aktas via groups.io]

[-- Attachment #1: Type: text/plain, Size: 4871 bytes --]

Same for TDX, I did not run it but it should cause failure
as debugShowPostCode is called OvmfPkg/ResetVector/Ia32/IntelTdx.asm before
actually the #VE handlers are installed.

-Erdem

On Wed, Jan 24, 2024 at 11:55 AM Tom Lendacky <thomas.lendacky@amd.com>
wrote:

> On 1/24/24 13:24, Tom Lendacky wrote:
> > On 1/24/24 10:47, Laszlo Ersek wrote:
> >> On 1/24/24 16:31, Gerd Hoffmann wrote:
> >>> Neat when doing ResetVector coding.
> >>>
> >>> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> >>> ---
> >>>   OvmfPkg/ResetVector/DebugCon.asm      | 43
> +++++++++++++++++++++++++++
> >>>   OvmfPkg/ResetVector/ResetVector.nasmb |  2 +-
> >>>   2 files changed, 44 insertions(+), 1 deletion(-)
> >>>   create mode 100644 OvmfPkg/ResetVector/DebugCon.asm
> >>>
> >>> diff --git a/OvmfPkg/ResetVector/DebugCon.asm
> >>> b/OvmfPkg/ResetVector/DebugCon.asm
> >>> new file mode 100644
> >>> index 000000000000..9c57d1a52c75
> >>> --- /dev/null
> >>> +++ b/OvmfPkg/ResetVector/DebugCon.asm
> >>> @@ -0,0 +1,43 @@
> >>>
> +;------------------------------------------------------------------------------
> >>> +; @file
> >>> +; qemu debug console support macros (based on serial port macros)
> >>> +;
> >>> +; Copyright (c) 2008 - 2018, Intel Corporation. All rights
> reserved.<BR>
> >>> +; SPDX-License-Identifier: BSD-2-Clause-Patent
> >>> +;
> >>>
> +;------------------------------------------------------------------------------
> >>> +
> >>> +%macro  outToDebugPort 1
> >>> +    mov     dx, 0x402
> >>> +    mov     al, %1
> >>> +    out     dx, al
> >>> +%endmacro
> >>> +
> >>> +%macro  debugShowCharacter 1
> >>> +    outToDebugPort %1
> >>> +%endmacro
> >>> +
> >>> +%macro  debugShowHexDigit 1
> >>> +  %if (%1 < 0xa)
> >>> +    debugShowCharacter BYTE ('0' + (%1))
> >>> +  %else
> >>> +    debugShowCharacter BYTE ('a' + ((%1) - 0xa))
> >>> +  %endif
> >>> +%endmacro
> >>> +
> >>> +%macro  debugNewline 0
> >>> +    debugShowCharacter `\r`
> >>> +    debugShowCharacter `\n`
> >>> +%endmacro
> >>> +
> >>> +%macro  debugShowPostCode 1
> >>> +    debugShowHexDigit (((%1) >> 4) & 0xf)
> >>> +    debugShowHexDigit ((%1) & 0xf)
> >>> +    debugNewline
> >>> +%endmacro
> >>> +
> >>> +BITS    16
> >>> +
> >>> +%macro  debugInitialize 0
> >>> +    ; not required
> >>> +%endmacro
> >>> diff --git a/OvmfPkg/ResetVector/ResetVector.nasmb
> >>> b/OvmfPkg/ResetVector/ResetVector.nasmb
> >>> index 5832aaa8abf7..f1655ddfcde3 100644
> >>> --- a/OvmfPkg/ResetVector/ResetVector.nasmb
> >>> +++ b/OvmfPkg/ResetVector/ResetVector.nasmb
> >>> @@ -41,7 +41,7 @@
> >>>   %elifdef DEBUG_SERIAL
> >>>     %include "SerialDebug.asm"
> >>>   %else
> >>> -  %include "DebugDisabled.asm"
> >>> +  %include "DebugCon.asm"
> >>>   %endif
> >>>   %include "Ia32/SearchForBfvBase.asm"
> >>
> >> (1) How much output does this produce? Trapping to QEMU for every single
> >> character written to the debug console is very slow. If it only produces
> >> a few bytes, that should be OK.
> >>
> >> (2) debugInitialize could actually be put to use; the presence of the
> >> QEMU debug console is detectable. We'd need to allocate a single byte
> >> somewhere, detect the console in debugInitialize, save the result in
> >> that byte, then check the byte in debugShowPostCode. Eliminates even
> >> those few (?) traps if there is no debug console configured.
> >>
> >> (3) I'm already hating myself for asking about this, but... is there a
> >> way for only customizing debugInitialize and debugShowCharacter? The
> >> rest is common with "SerialDebug.asm", and I wish I hadn't had to review
> >> those (unchanged) macros, they make my eyes bleed :/
> >>
> >> Anyway, if you think any of these (or all of these!) means too much
> >> work, I'm OK with the patch going-in as is.
> >
> > My concern would be around SEV-ES/SEV-SNP guest usage. The in and out
> > instruction will generate a #VC and would require a #VC handler to be in
> > place.
> >
> > I'm pretty sure this will cause issues for those types of guests, but it
> > might be a few days before I can get to it to verify. @Gerd, were you
> able
> > to test this with those types of guests?
>
> Had a meeting get canceled and so got a chance to test this. As I thought,
> this causes SEV-ES/SEV-SNP guest failures.
>
> Thanks,
> Tom
>
> >
> > Thanks,
> > Tom
> >
> >>
> >> I'm a bit concerned about (1), TBH.
> >>
> >> Laszlo
> >>
>


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Re: [edk2-devel] [PATCH 1/1] OvmfPkg/ResetVector: send post codes to qemu debug console

[Gerd Hoffmann]

On Wed, Jan 24, 2024 at 05:43:29PM -0800, Erdem Aktas wrote:
> Same for TDX, I did not run it but it should cause failure
> as debugShowPostCode is called OvmfPkg/ResetVector/Ia32/IntelTdx.asm before
> actually the #VE handlers are installed.
> 
> > Had a meeting get canceled and so got a chance to test this. As I thought,
> > this causes SEV-ES/SEV-SNP guest failures.

Hmm, I guess that pretty much kills the idea.  The first post code is
sent before probing for TDX/SEV happens ...

take care,
  Gerd



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Re: [edk2-devel] [PATCH 1/1] OvmfPkg/ResetVector: send post codes to qemu debug console

[Laszlo Ersek]

On 1/25/24 08:50, Gerd Hoffmann wrote:
> On Wed, Jan 24, 2024 at 05:43:29PM -0800, Erdem Aktas wrote:
>> Same for TDX, I did not run it but it should cause failure
>> as debugShowPostCode is called OvmfPkg/ResetVector/Ia32/IntelTdx.asm before
>> actually the #VE handlers are installed.
>>
>>> Had a meeting get canceled and so got a chance to test this. As I thought,
>>> this causes SEV-ES/SEV-SNP guest failures.
> 
> Hmm, I guess that pretty much kills the idea.  The first post code is
> sent before probing for TDX/SEV happens ...

Can we salvage it, but make it depend on a minimal source code tweak
(ungating)? Changing a single line for debugging (non-TDX / non-SEV-ES
guests, anyway) is much easier than coming up with this patch from zero,
whenever needed.

Can we add "DebugCon.asm" to the tree, plus a *comment* near

%include "DebugDisabled.asm"

about "DebugCon.asm"?

Thanks!
Laszlo



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Re: [edk2-devel] [PATCH 1/1] OvmfPkg/ResetVector: send post codes to qemu debug console

[Gerd Hoffmann]

On Thu, Jan 25, 2024 at 08:47:56PM +0100, Laszlo Ersek wrote:
> On 1/25/24 08:50, Gerd Hoffmann wrote:
> > On Wed, Jan 24, 2024 at 05:43:29PM -0800, Erdem Aktas wrote:
> >> Same for TDX, I did not run it but it should cause failure
> >> as debugShowPostCode is called OvmfPkg/ResetVector/Ia32/IntelTdx.asm before
> >> actually the #VE handlers are installed.
> >>
> >>> Had a meeting get canceled and so got a chance to test this. As I thought,
> >>> this causes SEV-ES/SEV-SNP guest failures.
> > 
> > Hmm, I guess that pretty much kills the idea.  The first post code is
> > sent before probing for TDX/SEV happens ...
> 
> Can we salvage it, but make it depend on a minimal source code tweak
> (ungating)? Changing a single line for debugging (non-TDX / non-SEV-ES
> guests, anyway) is much easier than coming up with this patch from zero,
> whenever needed.
> 
> Can we add "DebugCon.asm" to the tree, plus a *comment* near
> 
> %include "DebugDisabled.asm"
> 
> about "DebugCon.asm"?

Sure, can do that.  I assume the concern about the slowdown is moot if
this requires an source code patch to be enabled?

take care,
  Gerd



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Re: [edk2-devel] [PATCH 1/1] OvmfPkg/ResetVector: send post codes to qemu debug console

[Laszlo Ersek]

On 1/26/24 14:25, Gerd Hoffmann wrote:
> On Thu, Jan 25, 2024 at 08:47:56PM +0100, Laszlo Ersek wrote:
>> On 1/25/24 08:50, Gerd Hoffmann wrote:
>>> On Wed, Jan 24, 2024 at 05:43:29PM -0800, Erdem Aktas wrote:
>>>> Same for TDX, I did not run it but it should cause failure
>>>> as debugShowPostCode is called OvmfPkg/ResetVector/Ia32/IntelTdx.asm before
>>>> actually the #VE handlers are installed.
>>>>
>>>>> Had a meeting get canceled and so got a chance to test this. As I thought,
>>>>> this causes SEV-ES/SEV-SNP guest failures.
>>>
>>> Hmm, I guess that pretty much kills the idea.  The first post code is
>>> sent before probing for TDX/SEV happens ...
>>
>> Can we salvage it, but make it depend on a minimal source code tweak
>> (ungating)? Changing a single line for debugging (non-TDX / non-SEV-ES
>> guests, anyway) is much easier than coming up with this patch from zero,
>> whenever needed.
>>
>> Can we add "DebugCon.asm" to the tree, plus a *comment* near
>>
>> %include "DebugDisabled.asm"
>>
>> about "DebugCon.asm"?
> 
> Sure, can do that.  I assume the concern about the slowdown is moot if
> this requires an source code patch to be enabled?

Yes, absolutely! Since it's not enabled by default, only for dedicated
debugging sessions, the perf hit (if any) should be fine, IMO.

Laszlo



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