[edk2-devel] [RFC PATCH v2 38/44] UefiCpuPkg: Allow AP booting under SEV-ES
Andrew Fish via Groups.Io
afish=apple.com at groups.io
Thu Oct 10 23:56:04 UTC 2019
> On Oct 10, 2019, at 4:17 PM, Lendacky, Thomas <thomas.lendacky at amd.com> wrote:
>
> On 10/3/19 10:12 AM, Tom Lendacky wrote:
>>
>>
>> On 10/3/19 5:32 AM, Laszlo Ersek wrote:
>>> On 10/03/19 12:12, Laszlo Ersek wrote:
>>>
>>>> UINT32 ApEntryPoint;
>>>> EFI_GUID SevEsFooterGuid;
>>>> UINT16 Size;
>>>
>>> It's probably better to reverse the order of "Size" and
>>> "SevEsFooterGuid", like this:
>>>
>>> UINT32 ApEntryPoint;
>>> UINT16 Size;
>>> EFI_GUID SevEsFooterGuid;
>>>
>>> because then even the "Size" field can be changed (or resized), as a
>>> function of the footer GUID.
>>
>> Cool, I'll look into doing this and see how it works out.
>
> Just an update on this idea. This has worked out well, but has a couple of
> caveats. Removing the Qemu change to make the flash mapped read-only in
> the nested page tables, caused the following:
>
> 1. QemuFlashDetected() will attempt to detect how the flash memory device
> behaves. Because it is marked as read-only by the hypervisor, writing
> to the area results in a #NPF for the write-fault. With SEV-ES,
> emulation of the instruction can't be performed (can't read guest
> memory and not provided the faulting instruction bytes), so the vCPU is
> just restarted. This results in an infinite #NPF occurring.
>
> The solution here was to check for SEV-ES being enabled and just return
> false from QemuFlashDetected(). Any downfalls to doing that?
>
> 2. Commit 2db0ccc2d7fe ("UefiCpuPkg: Update CpuExceptionHandlerLib pass
> XCODE5 tool chain") causes a similar situation to #1. It attempts to do
> some address fixups and write to the flash device.
>
> Reverting that commit fixes the issue. I don't think that will be an
> acceptable solution, though, so need to think about what to do here.
>
Did you fill a bugzilla for 2)?
Thanks,
Andrew Fish
> After those two changes, the above method works well.
>
> Thanks,
> Tom
>
>>
>> Thanks!
>> Tom
>>
>>>
>>> Thanks
>>> Laszlo
>>>
>
>
>
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