Re: [edk2-devel] [Patch V4] UefiCpuPkg/MpInitLib: Enable execute disable bit.

["Gerd Hoffmann" <kraxel@redhat.com>]

On Mon, Nov 13, 2023 at 01:59:48PM +0800, xieyuanh wrote:
> From: Yuanhao Xie <yuanhao.xie@intel.com>
> 
> This patch synchronizes the No-Execute bit in the IA32_EFER
> register for the APs before the RestoreVolatileRegisters operation.
> 
> The commit 964a4f0, titled "Eliminate the second INIT-SIPI-SIPI
> sequence," replaces the second INIT-SIPI-SIPI sequence with the BSP
> calling the SwitchApContext function to initiate a specialized start-up
> signal, waking up APs in the DXE instead of using INIT-SIPI-SIPI.
> 
> Due to this change, the logic for "Enable execute disable bit" in
> MpFuncs.nasm is no longer executed. However, to ensure the proper setup
> of the page table, it is necessary to synchronize the IA32_EFER.NXE for
> APs before executing RestoreVolatileRegisters .
> 
> Based on SDM:
> If IA32_EFER.NXE is set to 1, it signifies execute-disable, meaning
> instruction fetches are not allowed from the 4-KByte page controlled by
> this entry. Conversely, if it is set to 0, it is reserved.
> 
> Signed-off-by: Yuanhao Xie <yuanhao.xie@intel.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Rahul Kumar <rahul1.kumar@intel.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>

Acked-by: Gerd Hoffmann <kraxel@redhat.com>



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