Re: [edk2-devel] [PATCH v9 08/46] UefiCpuPkg: Implement library support for VMGEXIT

["Lendacky, Thomas" <thomas.lendacky@amd.com>]

On 7/7/20 10:50 AM, Tom Lendacky wrote:
> On 7/7/20 10:36 AM, Laszlo Ersek wrote:
>> On 07/06/20 22:03, Tom Lendacky wrote:
>>> On 7/2/20 2:04 AM, Dong, Eric wrote:
>>>> Hi Tom,
>>>
>>> Hi Eric,
>>>
>>>>
>>>> We have root cause this Mac file format issue. The patch mail from your side include extra two "=0D=0D" , and our test tool convert them to "\r\r". This is Mac file line ending format. So this issue been reported. We have updated our tool to handle this special case.
>>>
>>> Good to know, thanks!
>>>
>>>>
>>>> With that change, now I met below error when use VS2015 tool chain. Can you help to fix it?
>>>>
>>>> Building ... g:\edk2-open-source\edk2\MdePkg\Library\PeiCoreEntryPoint\PeiCoreEntryPoint.inf [X64]
>>>> PeCoffLoaderEx.c
>>>> g:\edk2-open-source\edk2\OvmfPkg\Library\VmgExitLib\VmgExitVcHandler.c(386): warning C4334: '<<': result of 32-bit shift implicitly converted to 64 bits (was 64-bit shift intended?)
>>>> NMAKE : fatal error U1077: '"C:\Program Files (x86)\Microsoft Visual Studio 14.0\Vc\bin\x86_amd64\cl.exe"' : return code '0x2'
>>
>> This is for the line
>>
>>       Displacement *= (1 << Ext->Sib.Scale);
>>
>> from
>>
>>   [edk2-devel] [PATCH v9 17/46]
>>   OvmfPkg/VmgExitLib: Add support for NPF NAE events (MMIO)
>>
>>>
>>> Yup, looks like that needs to be a "1ULL <<" instead of "1 <<".
>>> I have verified that fixes the issue.
>>
>> I disagree.
>>
>> At that point, Displacement is of type INT64, and it may well be a
>> negative value. We definitely want to multiply it by a signed int
>> (values 1, 2, 4, 8).
>>
>> I commented on this before. Please see:
>>
>> (i) my comment block (10) here -- especially comment (10c):
>>
>>   https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fedk2.groups.io%2Fg%2Fdevel%2Fmessage%2F60144&amp;data=02%7C01%7Cthomas.lendacky%40amd.com%7Cec0cb2ad96694b66d8ff08d8228b7c8e%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637297329772337705&amp;sdata=g%2BGooY1Sv0G7ydr11Jh%2BTXxo4Wy6ZWcT5Mq9VmWddi8%3D&amp;reserved=0
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>> (alternative link:
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>>
>> (ii) and my comment here:
>>
>>   https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fedk2.groups.io%2Fg%2Fdevel%2Fmessage%2F60146&amp;data=02%7C01%7Cthomas.lendacky%40amd.com%7Cec0cb2ad96694b66d8ff08d8228b7c8e%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637297329772337705&amp;sdata=iNIBJCIlfEEsY37cdwUbH27tx5HvXVs3PZiOQfaGeLQ%3D&amp;reserved=0
>>
>> (alternative link:
>> <https://nam11.safelinks.protection.outlook.com/?url=http%3A%2F%2Fmid.mail-archive.com%2F139ce789-b938-c8b9-030e-c1b6c67e47ea%40redhat.com&amp;data=02%7C01%7Cthomas.lendacky%40amd.com%7Cec0cb2ad96694b66d8ff08d8228b7c8e%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637297329772337705&amp;sdata=mWCAHqTOpp7B9nWUJjTRJ9VZ74iwdElRTOoNhEpFs%2Bc%3D&amp;reserved=0>).
>>
>>
>> The compiler warning is well-meaning, but unnecessary. A 64-bit shift is
>> *NOT* intended. We want to end up with one of the signed int (aka INT32)
>> values 1, 2, 4 or 8. And then multiply the INT64 Displacement with that
>> value. For the multiplication, the INT32 value 1, 2, 4 or 8 will be
>> implicitly converted to INT64. That's entirely intentional.
>>
>> If we want to suppress the warning, while keeping the logic intact, we
>> should employ an explicit cast:
>>
>>   Displacement *= (INT64)(1 << Ext->Sib.Scale);
> 
> Ok, that makes sense. I'll use the explicit cast.
> 
>>
>>>
>>> One thing I noticed is that the 32-bit builds
>>> (PlatformCI_OvmfPkg_Windows_VS2019_PR, Platform_CI OVMF_IA32_NOOPT and
>>> Platform_CI OVMF_IA32X64_NOOPT) encounter an error:
>>>
>>> ERROR - Linker #2001 from SecMain.lib(SecMain.obj) :   unresolved external symbol __allshl
>>> ERROR - Linker #1120 from d:\a\1\s\Build\Ovmf3264\NOOPT_VS2019\IA32\OvmfPkg\Sec\SecMain\DEBUG\SecMain.dll : fatal   1 unresolved externals
>>> ERROR - Compiler #1077 from NMAKE : fatal   '"C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.26.28801\bin\Hostx86\x86\link.exe"' : return code '0x460'
>>>
>>> Any idea what is causing this error?
>>
>> A left-shift operator (<<) applied to a 64-bit operand is somehow
>> finding its way into the 32-bit SEC build.
>>
>> That is indeed wrong (for such cases, we're supposed to use LShiftU64()
>> from BaseLib).
>>
>> What I don't understand however is that all of the "<<" operator uses,
>> on 64-bit operands, should already be limited to code that is *only*
>> built for X64!
>>
>> For example, with this series applied, SecMain in OVMF consumes
>> "UefiCpuPkg/Library/CpuExceptionHandlerLib/SecPeiCpuExceptionHandlerLib.inf".
>> And the latter consumes VmgExitLib.
>>
>> But VmgExitLib is resolved to
>> "UefiCpuPkg/Library/VmgExitLibNull/VmgExitLibNull.inf", in the IA32 and
>> IA32X64 DSC files. This Null instance contains no left-shifts.
>>
>> Therefore any << operators, applied to 64-bit operands, present in
>> "OvmfPkg/Library/VmgExitLib", should never be compiled for IA32 and IA32X64.
>>
>> So I don't know where the problematic "<<" comes from. It does not come
>> from VmgExitLib, as far as I can tell.
> 
> Yes, I don't think it's coming from VmgExitLib, either.
> 
> I wonder if it somehow might be coming from the MSR_SEV_ES_GHCB_REGISTER
> struct and the bit fields that are used within it? That code, while not
> executed in non-X64 builds because SEV-ES is not active, is still built
> and maybe the bit fields result in implicit shifts occurring, specifically
> in SevEsProtocolFailure()?
> 
> I'll experiment with some things and see if that is the issue.

I commented out the setting of the GhcbTerminate fields in the
SevEsProtocolFailure() routine of OvmfPkg/Sec/SecMain.c and the error
disappeared. I'll see if changing from using UINT64 to multiple UINT32
entries fixes the problem, but I wouldn't think that the bit fields
would/should cause an issue here with 32-bit builds.

Thanks,
Tom

> 
> Thanks,
> Tom
> 
>>
>> Thanks,
>> Laszlo
>>