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To: Jiewen Yao <jiewen.yao@intel.com>, edk2-devel@ml01.01.org
References: <1480593847-3880-1-git-send-email-jiewen.yao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>,
 Jeff Fan <jeff.fan@intel.com>
From: Laszlo Ersek <lersek@redhat.com>
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Date: Thu, 1 Dec 2016 22:51:26 +0100
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 (mx1.redhat.com [10.5.110.30]); Thu, 01 Dec 2016 21:51:28 +0000 (UTC)
Subject: Re: [PATCH V2] UefiCpuPkg/PiSmmCpu: Fixed #double fault on #page fault.
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On 12/01/16 13:04, Jiewen Yao wrote:
> This patch fixes https://bugzilla.tianocore.org/show_bug.cgi?id=246
> 
> Previously, when SMM exception happens after EndOfDxe,
> with StackGuard enabled on IA32, the #double fault exception
> is reported instead of #page fault.
> 
> Root cause is below:
> 
> Current EDKII SMM page protection will lock GDT.
> If IA32 stack guard is enabled, the page fault handler will do task switch.
> This task switch need write busy flag in GDT, and write TSS.
> 
> However, the GDT and TSS is locked at that time, so the
> double fault happens.
> 
> We decide to not lock GDT for IA32 StackGuard enabled.
> 
> This issue does not exist on X64, or IA32 without StackGuard.
> 
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Jeff Fan <jeff.fan@intel.com>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Jiewen Yao <jiewen.yao@intel.com>
> ---
>  UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmmFuncsArch.c      | 55 ++++++++++++++++
>  UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h         | 68 ++++++++++++++++++++
>  UefiCpuPkg/PiSmmCpuDxeSmm/SmmCpuMemoryManagement.c | 48 --------------
>  UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c       | 49 +++++++++++++-
>  4 files changed, 171 insertions(+), 49 deletions(-)

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