* VMX HOST_RIP target alignment
@ 2022-11-17 20:46 Alexey Dobriyan
2022-11-17 23:22 ` Josh Poimboeuf
0 siblings, 1 reply; 2+ messages in thread
From: Alexey Dobriyan @ 2022-11-17 20:46 UTC (permalink / raw)
To: kvm; +Cc: linux-kernel, jpoimboe, pbonzini, x86
One of the side effects of fixing retbleed for VMX was demoting
HOST_RIP target from honorable function to a lowly label:
-SYM_FUNC_START(vmx_vmexit)
+SYM_INNER_LABEL(vmx_vmexit, SYM_L_GLOBAL)
ffffffff81243c49: 0f 01 c2 vmlaunch
ffffffff81243c4c: e9 a7 00 00 00 jmp ffffffff81243cf8 <vmx_vmexit+0xa7>
ffffffff81243c51 <vmx_vmexit>:
ffffffff81243c51: 50 push rax
Now I've never measured VM exit latency but is it important to align it
at 16 bytes like Intel recommends for functions?
vmalexey
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: VMX HOST_RIP target alignment
2022-11-17 20:46 VMX HOST_RIP target alignment Alexey Dobriyan
@ 2022-11-17 23:22 ` Josh Poimboeuf
0 siblings, 0 replies; 2+ messages in thread
From: Josh Poimboeuf @ 2022-11-17 23:22 UTC (permalink / raw)
To: Alexey Dobriyan; +Cc: kvm, linux-kernel, pbonzini, x86
On Thu, Nov 17, 2022 at 11:46:09PM +0300, Alexey Dobriyan wrote:
> One of the side effects of fixing retbleed for VMX was demoting
> HOST_RIP target from honorable function to a lowly label:
>
> -SYM_FUNC_START(vmx_vmexit)
> +SYM_INNER_LABEL(vmx_vmexit, SYM_L_GLOBAL)
>
> ffffffff81243c49: 0f 01 c2 vmlaunch
> ffffffff81243c4c: e9 a7 00 00 00 jmp ffffffff81243cf8 <vmx_vmexit+0xa7>
>
> ffffffff81243c51 <vmx_vmexit>:
> ffffffff81243c51: 50 push rax
>
> Now I've never measured VM exit latency but is it important to align it
> at 16 bytes like Intel recommends for functions?
Yes, I'd think we should restore the alignment to 16 bytes again, that
change was definitely not intentional.
--
Josh
^ permalink raw reply [flat|nested] 2+ messages in thread
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