Re: [Xen-devel] XSAVE/XRSTOR crash resurgence in 4.3

[Ben Guthro <ben.guthro@xxxxxxxxx>]

On Wed, Jul 17, 2013 at 2:38 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>> On 16.07.13 at 18:57, Ben Guthro <ben.guthro@xxxxxxxxx> wrote:
>> On Tue, Jul 16, 2013 at 12:23 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>>>> On 15.07.13 at 15:49, Ben Guthro <ben.guthro@xxxxxxxxx> wrote:
>>>> The following output was from a WinXP SP3 guest (32bit) on a Lenovo T430:
>>>>
>>>> (XEN) d1v0: fip=1b773d6e9a fdp=23773d1c48 w=8
>>>> (XEN) d1v0: FIP=1b773d6e9a FDP=23773d1c48 w=8
>>>> (XEN) d1v1: fip=1b79e78dee fdp=230012e3b4 w=8
>>>> (XEN) d1v1: FIP=1b79e78dee FDP=230012e3b4 w=8
>>>> (XEN) d1v1: fip=0000:79e78dee fdp=0000:0012e3b4
>>>> (XEN) d1v1: fip=0000:79e78dee fdp=0000:0012e3b4
>>>> (XEN) d1v1: fip=0000:79e78dee fdp=0000:0012e3b4
>>>> (XEN) d1v1: fip=0000:79e78dee fdp=0000:0012e3b4
>>>> (XEN) d1v1: fip=1b79e78dee fdp=230012d528 w=8
>>>> (XEN) d1v1: FIP=1b79e78dee FDP=230012d528 w=8
>>>> (XEN) d1v0: fip=4500000000 fdp=4b1000000000 w=8
>>>> (XEN) d1v0: FIP=4500000000 FDP=4b1000000000 w=8
>>>> (XEN) d1v1: fip=1b773d6e9a fdp=23773d1c48 w=8
>>>> (XEN) d1v1: FIP=1b773d6e9a FDP=23773d1c48 w=8
>>>
>>> Well, it should have been quite obvious (to me) that this is
>>> related to xsaveopt behavior (according to my own observations
>>> of cases where the selector/offset fields don't get written). Could
>>> you double check whether the system(s) you see the problem on
>>> support xsaveopt, and if so, simply comment out the conditionals
>>> that cause it to be used?
>>
>> They do support xsaveopt.
>> I'll ifdef these out for tonight's test run.

There was a problem with my commit for this test run, so I did not get
the data I wanted.

I will test with this patch tonight.
Thank you

Ben

>
> And attached/below also a tentative fix.
>
> Jan
>
> --- a/xen/arch/x86/xstate.c
> +++ b/xen/arch/x86/xstate.c
> @@ -72,9 +72,24 @@ void xsave(struct vcpu *v, uint64_t mask
>      if ( word_size <= 0 || !is_pv_32bit_vcpu(v) )
>      {
>          if ( cpu_has_xsaveopt )
> +        {
> +            /*
> +             * xsaveopt may not write the FPU portion even when the 
> respective
> +             * mask bit is set. For the check further down to work we hence
> +             * need to put the save image back into the state that it was in
> +             * right after the previous xsaveopt.
> +             */
> +            if ( word_size > 0 &&
> +                 (ptr->fpu_sse.x[FPU_WORD_SIZE_OFFSET] == 4 ||
> +                  ptr->fpu_sse.x[FPU_WORD_SIZE_OFFSET] == 2) )
> +            {
> +                ptr->fpu_sse.fip.sel = 0;
> +                ptr->fpu_sse.fdp.sel = 0;
> +            }
>              asm volatile ( ".byte 0x48,0x0f,0xae,0x37"
>                             : "=m" (*ptr)
>                             : "a" (lmask), "d" (hmask), "D" (ptr) );
> +        }
>          else
>              asm volatile ( ".byte 0x48,0x0f,0xae,0x27"
>                             : "=m" (*ptr)
>
>

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