[edk2-devel] [PATCH] UefiCpuPkg/MpInitLib: Allocate a separate SEV-ES AP reset stack area
Marvin Häuser
mhaeuser at posteo.de
Fri May 14 15:04:42 UTC 2021
Good day Thomas,
Thank you very much for the quick patch. Comments inline.
Best regards,
Marvin
On 11.05.21 22:50, Lendacky, Thomas wrote:
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3324
>
> The SEV-ES stacks currently share a page with the reset code and data.
> Separate the SEV-ES stacks from the reset vector code and data to avoid
> possible stack overflows from overwriting the code and/or data.
>
> When SEV-ES is enabled, invoke the GetWakeupBuffer() routine a second time
> to allocate a new area, below the reset vector and data.
>
> Both the PEI and DXE versions of GetWakeupBuffer() are changed to track
> the previous reset buffer allocation in order to ensure that the new
> buffer allocation is below the previous allocation.
>
> Fixes: 7b7508ad784d16a5208c8d12dff43aef6df0835b
> Cc: Eric Dong <eric.dong at intel.com>
> Cc: Ray Ni <ray.ni at intel.com>
> Cc: Laszlo Ersek <lersek at redhat.com>
> Cc: Rahul Kumar <rahul1.kumar at intel.com>
> Signed-off-by: Tom Lendacky <thomas.lendacky at amd.com>
> ---
> UefiCpuPkg/Library/MpInitLib/DxeMpLib.c | 12 ++++-
> UefiCpuPkg/Library/MpInitLib/MpLib.c | 48 +++++++++++++-------
> UefiCpuPkg/Library/MpInitLib/PeiMpLib.c | 14 ++++--
> 3 files changed, 54 insertions(+), 20 deletions(-)
>
> diff --git a/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c b/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c
> index 7839c249760e..fdfa0755d37a 100644
> --- a/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c
> +++ b/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c
> @@ -29,6 +29,11 @@ VOID *mReservedApLoopFunc = NULL;
> UINTN mReservedTopOfApStack;
> volatile UINT32 mNumberToFinish = 0;
>
> +//
> +// Begin wakeup buffer allocation below 0x88000
> +//
This definitely is not an issue of your patch at all, but I find the
comments of the behaviour very lacking. Might this be a good opportunity
to briefly document it? It took me quite a bit of git blame to fully
figure it out, especially due to the non-descriptive commit message. The
constant is explained very well in the description:
https://github.com/tianocore/edk2/commit/e4ff6349bf9ee4f3f392141374901ea4994e043e
> +STATIC EFI_PHYSICAL_ADDRESS mWakeupBuffer = 0x88000;
Hmm, I wonder whether a global variable is the best solution here. With
an explanation from the commit above, a top-down allocator makes good
sense for this scenario. However, a "GetWakeupBuffer(Size, MaxAddress)"
function might be more self-descriptive. What do you think?
> +
> /**
> Enable Debug Agent to support source debugging on AP function.
>
> @@ -102,7 +107,7 @@ GetWakeupBuffer (
> // LagacyBios driver depends on CPU Arch protocol which guarantees below
> // allocation runs earlier than LegacyBios driver.
> //
> - StartAddress = 0x88000;
> + StartAddress = mWakeupBuffer;
> Status = gBS->AllocatePages (
> AllocateMaxAddress,
> MemoryType,
> @@ -112,6 +117,11 @@ GetWakeupBuffer (
> ASSERT_EFI_ERROR (Status);
> if (EFI_ERROR (Status)) {
> StartAddress = (EFI_PHYSICAL_ADDRESS) -1;
> + } else {
> + //
> + // Next wakeup buffer allocation must be below this allocation
> + //
> + mWakeupBuffer = StartAddress;
> }
>
> DEBUG ((DEBUG_INFO, "WakeupBufferStart = %x, WakeupBufferSize = %x\n",
> diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> index dc2a54aa31e8..a76dae437606 100644
> --- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
> +++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> @@ -1164,20 +1164,6 @@ GetApResetVectorSize (
> AddressMap->SwitchToRealSize +
> sizeof (MP_CPU_EXCHANGE_INFO);
>
> - //
> - // The AP reset stack is only used by SEV-ES guests. Do not add to the
> - // allocation if SEV-ES is not enabled.
> - //
> - if (PcdGetBool (PcdSevEsIsEnabled)) {
> - //
> - // Stack location is based on APIC ID, so use the total number of
> - // processors for calculating the total stack area.
> - //
> - Size += AP_RESET_STACK_SIZE * PcdGet32 (PcdCpuMaxLogicalProcessorNumber);
> -
> - Size = ALIGN_VALUE (Size, CPU_STACK_ALIGNMENT);
> - }
> -
> return Size;
> }
>
> @@ -1207,9 +1193,39 @@ AllocateResetVector (
> CpuMpData->AddressMap.ModeTransitionOffset
> );
> //
> - // The reset stack starts at the end of the buffer.
> + // The AP reset stack is only used by SEV-ES guests. Do not allocate it
> + // if SEV-ES is not enabled.
> //
> - CpuMpData->SevEsAPResetStackStart = CpuMpData->WakeupBuffer + ApResetVectorSize;
> + if (PcdGetBool (PcdSevEsIsEnabled)) {
> + UINTN ApResetStackSize;
Personally, I do not mind this at all, but I think the code style
prohibits declaring variables in inner scopes. Though preferably I would
like to see this, nowadays, arbitrary restriction lifted rather than the
patch be changed. Do the package maintainers have comments on this?
> +
> + //
> + // Stack location is based on ProcessorNumber, so use the total number
> + // of processors for calculating the total stack area.
> + //
> + ApResetStackSize = AP_RESET_STACK_SIZE *
> + PcdGet32 (PcdCpuMaxLogicalProcessorNumber);
> +
> + //
> + // Invoke GetWakeupBuffer a second time to allocate the stack area
> + // below 1MB. The returned buffer will be page aligned and sized and
> + // below the previously allocated buffer.
> + //
> + CpuMpData->SevEsAPResetStackStart = GetWakeupBuffer (ApResetStackSize);
> +
> + //
> + // Check to be sure that the "allocate below" behavior hasn't changed.
> + // This will also catch a failed allocation, as "-1" is returned on
> + // failure.
> + //
> + if (CpuMpData->SevEsAPResetStackStart >= CpuMpData->WakeupBuffer) {
> + DEBUG ((DEBUG_ERROR,
> + "SEV-ES AP reset stack is not below wakeup buffer\n"));
> +
> + ASSERT (FALSE);
Should the ASSERT not only catch the broken "allocate below" behaviour,
i.e. not trigger on failed allocation?
> + CpuDeadLoop ();
> + }
> + }
> }
> BackupAndPrepareWakeupBuffer (CpuMpData);
> }
> diff --git a/UefiCpuPkg/Library/MpInitLib/PeiMpLib.c b/UefiCpuPkg/Library/MpInitLib/PeiMpLib.c
> index 3989bd6a7a9f..4d09e89b4128 100644
> --- a/UefiCpuPkg/Library/MpInitLib/PeiMpLib.c
> +++ b/UefiCpuPkg/Library/MpInitLib/PeiMpLib.c
> @@ -11,6 +11,8 @@
> #include <Guid/S3SmmInitDone.h>
> #include <Ppi/ShadowMicrocode.h>
>
> +STATIC UINT64 mWakeupBuffer = BASE_1MB;
> +
> /**
> S3 SMM Init Done notification function.
>
> @@ -220,11 +222,11 @@ GetWakeupBuffer (
> // Need memory under 1MB to be collected here
> //
> WakeupBufferEnd = Hob.ResourceDescriptor->PhysicalStart + Hob.ResourceDescriptor->ResourceLength;
> - if (WakeupBufferEnd > BASE_1MB) {
> + if (WakeupBufferEnd > mWakeupBuffer) {
> //
> - // Wakeup buffer should be under 1MB
> + // Wakeup buffer should be under 1MB and under the previous one
> //
> - WakeupBufferEnd = BASE_1MB;
> + WakeupBufferEnd = mWakeupBuffer;
> }
> while (WakeupBufferEnd > WakeupBufferSize) {
> //
> @@ -244,6 +246,12 @@ GetWakeupBuffer (
> }
> DEBUG ((DEBUG_INFO, "WakeupBufferStart = %x, WakeupBufferSize = %x\n",
> WakeupBufferStart, WakeupBufferSize));
> +
> + //
> + // Next wakeup buffer allocation must be below this allocation
> + //
> + mWakeupBuffer = WakeupBufferStart;
> +
> return (UINTN)WakeupBufferStart;
> }
> }
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