linux-kernel - Re: [PATCH 2/2] deal with interrupt shadow state for emulated instruction

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Message-ID: <4A09BC90.9030700@redhat.com>
Date:	Tue, 12 May 2009 21:14:40 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Glauber Costa <glommer@...hat.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>, Gleb Natapov <gleb@...hat.com>
Subject: Re: [PATCH 2/2] deal with interrupt shadow state for emulated instruction

Glauber Costa wrote:
> we currently unblock shadow interrupt state when we skip an instruction,
> but failing to do so when we actually emulate one. This blocks interrupts
> in key instruction blocks, in particular sti; hlt; sequences
>
> If the instruction emulated is an sti, we have to block shadow interrupts.
> The same goes for mov ss. pop ss also needs it, but we don't currently
> emulate it.
>
> Without this patch, I cannot boot gpxe option roms at vmx machines.
> This is described at https://bugzilla.redhat.com/show_bug.cgi?id=494469
>
> @@ -1618,6 +1620,15 @@ special_insn:
>  		int err;
>  
>  		sel = c->src.val;
> +		if (c->modrm_reg == VCPU_SREG_SS) {
> +			u32 int_shadow =
> +			kvm_x86_ops->get_interrupt_shadow(ctxt->vcpu,
> +							  X86_SHADOW_INT_MOV_SS);
> +			/* See sti emulation for an explanation of this */
> +			if (!(int_shadow & X86_SHADOW_INT_MOV_SS))
> +				ctxt->interruptibility = X86_SHADOW_INT_MOV_SS;
> +		}
>   

The indentation of the first statement here is annoying.  Suggest a 
function toggle_interruptibility(ctxt, mask).  Would eliminate the need 
for the comment forward reference as well.


-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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