Re: [PATCH v2] ArmVirtPkg/PlatformHasAcpiDtDxe: allow guest level ACPI disable override

[Laszlo Ersek <lersek@redhat.com>]

On 03/29/17 19:50, Ard Biesheuvel wrote:
> In general, we should not present two separate (and inevitably different)
> hardware descriptions to the OS, in the form of ACPI tables and a device
> tree blob. For this reason, we recently added the logic to ArmVirtQemu to
> only expose the ACPI 2.0 entry point if no DT binary is being passed, and
> vice versa.
> 
> However, this is arguably a regression for those who relied on DT
> descriptions being available, even if the former behavior can be
> restored by passing the -no-acpi switch to QEMU.
> 
> So allow a secret handshake with the UEFI Shell, to set a variable that
> will result in ACPI to be disabled on subsequent boots even if -no-acpi
> was not passed on the QEMU command line.
> 
>   setvar -nv -bs -guid 50bea1e5-a2c5-46e9-9b3a-59596516b00a ForceNoAcpi =01
> 
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  ArmVirtPkg/ArmVirtPkg.dec                                | 9 +++++++++
>  ArmVirtPkg/ArmVirtQemu.dsc                               | 3 +++
>  ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.c   | 2 ++
>  ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.inf | 5 +++++
>  4 files changed, 19 insertions(+)
> 
> diff --git a/ArmVirtPkg/ArmVirtPkg.dec b/ArmVirtPkg/ArmVirtPkg.dec
> index efe83a383d55..a8603e1b80e5 100644
> --- a/ArmVirtPkg/ArmVirtPkg.dec
> +++ b/ArmVirtPkg/ArmVirtPkg.dec
> @@ -34,6 +34,8 @@ [Guids.common]
>    gArmVirtTokenSpaceGuid = { 0x0B6F5CA7, 0x4F53, 0x445A, { 0xB7, 0x6E, 0x2E, 0x36, 0x5B, 0x80, 0x63, 0x66 } }
>    gEarlyPL011BaseAddressGuid       = { 0xB199DEA9, 0xFD5C, 0x4A84, { 0x80, 0x82, 0x2F, 0x41, 0x70, 0x78, 0x03, 0x05 } }
>  
> +  gArmVirtVariableGuid   = { 0x50bea1e5, 0xa2c5, 0x46e9, { 0x9b, 0x3a, 0x59, 0x59, 0x65, 0x16, 0xb0, 0x0a } }
> +
>  [Protocols]
>    gFdtClientProtocolGuid = { 0xE11FACA0, 0x4710, 0x4C8E, { 0xA7, 0xA2, 0x01, 0xBA, 0xA2, 0x59, 0x1B, 0x4C } }
>  
> @@ -58,3 +60,10 @@ [PcdsFixedAtBuild, PcdsPatchableInModule]
>    # EFI_VT_100_GUID.
>    #
>    gArmVirtTokenSpaceGuid.PcdTerminalTypeGuidBuffer|{0x65, 0x60, 0xA6, 0xDF, 0x19, 0xB4, 0xD3, 0x11, 0x9A, 0x2D, 0x00, 0x90, 0x27, 0x3F, 0xC1, 0x4D}|VOID*|0x00000007
> +
> +[PcdsDynamic]
> +  #
> +  # Whether to force disable ACPI, regardless of the fw_cfg settings
> +  # exposed by QEMU
> +  #
> +  gArmVirtTokenSpaceGuid.PcdForceNoAcpi|0x0|BOOLEAN|0x00000003
> diff --git a/ArmVirtPkg/ArmVirtQemu.dsc b/ArmVirtPkg/ArmVirtQemu.dsc
> index 4075b92aa2cb..76a7908105ab 100644
> --- a/ArmVirtPkg/ArmVirtQemu.dsc
> +++ b/ArmVirtPkg/ArmVirtQemu.dsc
> @@ -210,6 +210,9 @@ [PcdsDynamicDefault.common]
>    gEfiMdeModulePkgTokenSpaceGuid.PcdSmbiosDocRev|0x0
>    gUefiOvmfPkgTokenSpaceGuid.PcdQemuSmbiosValidated|FALSE
>  
> +[PcdsDynamicHii]
> +  gArmVirtTokenSpaceGuid.PcdForceNoAcpi|L"ForceNoAcpi"|gArmVirtVariableGuid|0x0|FALSE|NV,BS
> +
>  ################################################################################
>  #
>  # Components Section - list of all EDK II Modules needed by this Platform
> diff --git a/ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.c b/ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.c
> index 8932dacabec5..da3cee645cfb 100644
> --- a/ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.c
> +++ b/ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.c
> @@ -17,6 +17,7 @@
>  #include <Guid/PlatformHasDeviceTree.h>
>  #include <Library/BaseLib.h>
>  #include <Library/DebugLib.h>
> +#include <Library/PcdLib.h>
>  #include <Library/QemuFwCfgLib.h>
>  #include <Library/UefiBootServicesTableLib.h>
>  
> @@ -37,6 +38,7 @@ PlatformHasAcpiDt (
>    // errors here.
>    //
>    if (MAX_UINTN == MAX_UINT64 &&
> +      !PcdGetBool (PcdForceNoAcpi) &&
>        !EFI_ERROR (
>           QemuFwCfgFindFile (
>             "etc/table-loader",
> diff --git a/ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.inf b/ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.inf
> index 4466bead57c2..08025f0c3722 100644
> --- a/ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.inf
> +++ b/ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.inf
> @@ -25,6 +25,7 @@ [Sources]
>    PlatformHasAcpiDtDxe.c
>  
>  [Packages]
> +  ArmVirtPkg/ArmVirtPkg.dec
>    EmbeddedPkg/EmbeddedPkg.dec
>    MdePkg/MdePkg.dec
>    OvmfPkg/OvmfPkg.dec
> @@ -32,6 +33,7 @@ [Packages]
>  [LibraryClasses]
>    BaseLib
>    DebugLib
> +  PcdLib
>    QemuFwCfgLib
>    UefiBootServicesTableLib
>    UefiDriverEntryPoint
> @@ -40,5 +42,8 @@ [Guids]
>    gEdkiiPlatformHasAcpiGuid       ## SOMETIMES_PRODUCES ## PROTOCOL
>    gEdkiiPlatformHasDeviceTreeGuid ## SOMETIMES_PRODUCES ## PROTOCOL
>  
> +[Pcd]
> +  gArmVirtTokenSpaceGuid.PcdForceNoAcpi
> +
>  [Depex]
>    TRUE
> 

Technically the patch is sound. I continue to disagree with its goal though.

Technically, the patch could be improved (towards its wrong goal) by
exposing the boolean knob with an HII checkbox, called "disable ACPI
regardless of what the QEMU command line says". That would mirror Marc's
comments from earlier.

For now, I actually agree with you that we shouldn't expose the knob
through HII however. Your reason for not doing HII is to mitigate what
you perceive as a regression as quickly as possible. My reason is that I
want to keep this loophole out of public view as much as possible, and
the UEFI shell is arguably harder to approach than an HII form.

* Please extend the commit message with the UEFI shell command that
closes the loophole again.

* Also, please get Marc and Mark to ACK this patch, using their @arm.com
email addresses. (I wish I could get Leif to ACK the patch as well, but
he's on vacation.)

* Finally, please add:

Abstained-by: Laszlo Ersek <lersek@redhat.com>

before pushing the patch.

The commit log has to show that ARM people were okay with this, and that
my own self was opposed. I generally abhor regressions, but in this case
I feel the risk for the ecosystem is too large, so abstaining (in a
documented way) is the best I can do for you now. I'll re-state for one
last time that IMO this patch will contribute to the fragmentation that
we see in the hardware description space.

(We'll revert the patch in RH downstream.)

Laszlo