Re: KVM: Fix the invlpg instruction emulation on AMD64

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Aurelien Jarno wrote:
> The patch below removes the check for c->modrm_reg == 7 to detect the 
> invlpg instruction, as it was the case before before commit 
> aa38840d3d2e0a804e628077df8d8879b496d741. This fixes the boot of FreeBSD
> on an AMD64 CPU.
>
> It also moves the assignation of c->src.bytes after the test as it is
> not needed for the invlpg instruction.
>
> Signed-off-by: Aurelien Jarno <aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org>
>
> diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
> index fa33fcd..01aa952 100644
> --- a/drivers/kvm/x86_emulate.c
> +++ b/drivers/kvm/x86_emulate.c
> @@ -824,12 +824,10 @@ modrm_done:
>  		c->src.bytes = 4;
>  		goto srcmem_common;
>  	case SrcMem:
> -		c->src.bytes = (c->d & ByteOp) ? 1 :
> -							   c->op_bytes;
>  		/* Don't fetch the address for invlpg: it could be unmapped. */
> -		if (c->twobyte && c->b == 0x01
> -				    && c->modrm_reg == 7)
> +		if (c->twobyte && c->b == 0x01)
>  			break;
> +		c->src.bytes = (c->d & ByteOp) ? 1 : c->op_bytes;
>
>   

I don't understand why this helps.  All of the other instructions in 
this group either have modrm_mod == 3 or do require evaluation of the 
source.  invlpg is the only one that doesn't.

It looks like this patch would break lgdt and lidt (which are only 
needed on Intel).

-- 
error compiling committee.c: too many arguments to function


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