Laszlo:
Yes. This solution makes sense.
Thanks
Liming
-----Original Message-----
From: Laszlo Ersek <[email protected]>
Sent: 2020年7月28日 23:19
To: Tom Lendacky <[email protected]>; Gao, Liming <[email protected]>;
[email protected]
Cc: Brijesh Singh <[email protected]>; Ard Biesheuvel
<[email protected]>; Dong, Eric <[email protected]>; Justen, Jordan L
<[email protected]>; Kinney, Michael D <[email protected]>;
Ni, Ray <[email protected]>
Subject: Re: [PATCH v12 07/46] MdePkg/BaseLib: Add support for the VMGEXIT
instruction
On 07/28/20 16:13, Tom Lendacky wrote:
> IIUC, create a VmgExit.c file in MdePkg/Library/BaseLib/Ia32/ that
> doesn't actually encode the VMGEXIT instruction, just calls
> CpuBreakpoint(), e.g.:
>
> VOID
> EFIAPI
> AsmVmgExit (
> VOID
> )
> {
> CpuBreakpoint();
> }
>
Yes -- either that, or even just open-code (copy) what we have in
MdePkg/Library/BaseLib/Ia32/CpuBreakpoint.nasm
now:
global ASM_PFX(AsmVmgExit)
ASM_PFX(AsmVmgExit):
;
; VMGEXIT makes no sense on IA32, and NASM versions before 2.12 cannot ;
translate the 64-bit "rep vmmcall" instruction into elf32 format. So ; provide
a stub implementation that is identical to CpuBreakpoint(). In ; practice,
AsmVmgExit() should never be called on IA32.
;
int 3
ret
Because this assembly-language implementation might be more "true" to the name
"AsmVmgExit".
Liming, would you be OK with this approach? In other words, the set of files
changed/introduced in this patch would not change, just the implementation of
IA32 AsmVmgExit().
> The other alternative is to use a DB-encoded instruction, though I
> know that isn't the most popular approach.
Right, I've been quite on a quest to eliminate DBs that encode instructions.
> The BITS 64 method to generate the instruction bytes is also used in
> OvmfPkg/ResetVector/Ia32/PageTables64.asm, but that file is only
> included when ARCH_X64 is defined, so there shouldn't be an issue
> there, plus the nasm file format is bin (-f bin).
I confirm that; the following commands all work on RHEL7, with this series
applied:
$ build -b NOOPT -t GCC48 -m OvmfPkg/ResetVector/ResetVector.inf -a IA32
-p OvmfPkg/OvmfPkgIa32.dsc
$ build -b NOOPT -t GCC48 -m OvmfPkg/ResetVector/ResetVector.inf -a IA32 -a X64
-p OvmfPkg/OvmfPkgIa32X64.dsc
$ build -b NOOPT -t GCC48 -m OvmfPkg/ResetVector/ResetVector.inf -a X64
-p OvmfPkg/OvmfPkgX64.dsc
Thanks!
Laszlo
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