Re: [Xen-devel] [PATCH v3 18/24] x86/shadow: Avoid raising faults behind the emulators back

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.11.16 at 14:50, <andrew.cooper3@xxxxxxxxxx> wrote:
> --- a/xen/arch/x86/mm/shadow/multi.c
> +++ b/xen/arch/x86/mm/shadow/multi.c
> @@ -3373,18 +3373,35 @@ static int sh_page_fault(struct vcpu *v,
>  
>      r = x86_emulate(&emul_ctxt.ctxt, emul_ops);
>  
> -    /*
> -     * The previous lack of inject_{sw,hw}*() hooks caused exceptions raised
> -     * by the emulator itself to become X86EMUL_UNHANDLEABLE.  Such 
> exceptions
> -     * now set event_pending instead.  Exceptions raised behind the back of
> -     * the emulator don't yet set event_pending.
> -     *
> -     * For now, cause such cases to return to the X86EMUL_UNHANDLEABLE path,
> -     * for no functional change from before.  Future patches will fix this
> -     * properly.
> -     */
>      if ( r == X86EMUL_EXCEPTION && emul_ctxt.ctxt.event_pending )
> -        r = X86EMUL_UNHANDLEABLE;
> +    {
> +        /*
> +         * This emulation covers writes to shadow pagetables.  We tolerate 
> #PF
> +         * (from hitting adjacent pages) and #GP/#SS (from segmentation
> +         * errors).  Anything else is an emulation bug, or a guest playing
> +         * with the instruction stream under Xen's feet.
> +         */

Same comment here regarding "adjacent".

> +        if ( emul_ctxt.ctxt.event.type == X86_EVENTTYPE_HW_EXCEPTION &&
> +             (emul_ctxt.ctxt.event.vector < 32) &&
> +             ((1u << emul_ctxt.ctxt.event.vector) &
> +              ((1u << TRAP_stack_error) | (1u << TRAP_gp_fault) |
> +               (1u << TRAP_page_fault))) )

May I suggest to also demand an error code of zero for #GP/#SS?

> +        {
> +            if ( is_hvm_vcpu(v) )

has_hvm_container_domain()?

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel