On 03/12/2014 19:45, Radim Krčmář wrote:
> 2014-12-03 15:26+0100, Paolo Bonzini:
>>
>>
>> On 03/12/2014 15:23, Nadav Amit wrote:
>>> I think it is better just to replace the last line with:
>>>
>>> *(u64 *)(dest + XSAVE_HDR_OFFSET) = xsave->xsave_hdr.xstate_bv
>
> Yeah, or we can use this value for xstate_bv to save some copying too,
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 19e5e8f..ba2b7bd 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3137,7 +3137,7 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct
> kvm_vcpu *vcpu,
> static void fill_xsave(u8 *dest, struct kvm_vcpu *vcpu)
> {
> struct xsave_struct *xsave = &vcpu->arch.guest_fpu.state->xsave;
> - u64 xstate_bv = vcpu->arch.guest_supported_xcr0 | XSTATE_FPSSE;
> + u64 xstate_bv = xsave->xsave_hdr.xstate_bv;
Also good.
> u64 valid;
>
> /*
>
>> Right, this matches
>>
>> u64 xstate_bv = *(u64 *)(src + XSAVE_HDR_OFFSET);
>> ...
>> xsave->xsave_hdr.xstate_bv = xstate_bv;
>>
>> in load_xsave.
>
> Btw, we don't care about crashers from userspace?
We do, but they're taken care of by
if (xstate_bv & ~kvm_supported_xcr0())
return -EINVAL;
in kvm_vcpu_ioctl_x86_set_xsave. kvm_supported_xcr0 is always a subset
of host_xcr0, hence:
> /* Set XSTATE_BV and possibly XCOMP_BV. */
> xsave->xsave_hdr.xstate_bv = xstate_bv;
> - if (cpu_has_xsaves)
> + if (cpu_has_xsaves) {
> xsave->xsave_hdr.xcomp_bv = host_xcr0 |
> XSTATE_COMPACTION_ENABLED;
> + xsave->xsave_hdr.xstate_bv &= xsave->xsave_hdr.xcomp_bv;
this is not zeroing any bit. Thanks for thinking about it, though. :)
Paolo
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