Re: [edk2-devel] [PATCH] UefiCpuPkg/CpuExceptionHandlerLib: Fix #AC split lock

["Dong, Eric" <eric.dong@intel.com>]

Hi John,

I'm not sure whether I understand the code correctly. If not, please correct me.

1. You change to the code to only exchange 32 bits(eax) instead of 64 bits(rax). After your change, how to handle the above 32 bits value (from bit 32 to bit 63)?
2. In this file, also have another two xchg codes, do them need to be updated also?

Thanks,
Eric
> -----Original Message-----
> From: devel@edk2.groups.io [mailto:devel@edk2.groups.io] On Behalf Of John
> E Lofgren
> Sent: Wednesday, September 4, 2019 2:15 AM
> To: devel@edk2.groups.io
> Subject: [edk2-devel] [PATCH] UefiCpuPkg/CpuExceptionHandlerLib: Fix #AC
> split lock
> 
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2150
> 
> Fix #AC split lock's caused by seperating base and limit from sgdt and sidt by
> changing xchg operands to 32-bit to stop from crossing cacheline.
> 
> Signed-off-by: John E Lofgren <john.e.lofgren@intel.com>
> ---
>  UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.nasm
> | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git
> a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.nas
> m
> b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.nas
> m
> index 4db1a09f28..6d83dca4b9 100644
> ---
> a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.nas
> m
> +++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.
> +++ nasm
> @@ -184,17 +184,17 @@ HasErrorCode:
>      push    rax
>      push    rax
>      sidt    [rsp]
> -    xchg    rax, [rsp + 2]
> -    xchg    rax, [rsp]
> -    xchg    rax, [rsp + 8]
> +    xchg    eax, [rsp + 2]
> +    xchg    eax, [rsp]
> +    xchg    eax, [rsp + 8]
> 
>      xor     rax, rax
>      push    rax
>      push    rax
>      sgdt    [rsp]
> -    xchg    rax, [rsp + 2]
> -    xchg    rax, [rsp]
> -    xchg    rax, [rsp + 8]
> +    xchg    eax, [rsp + 2]
> +    xchg    eax, [rsp]
> +    xchg    eax, [rsp + 8]
> 
>  ;; UINT64  Ldtr, Tr;
>      xor     rax, rax
> --
> 2.16.2.windows.1
> 
> 
>