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SubjectRe: [CFT PATCH 2/2] KVM: x86: support XSAVES usage in the host
On 11/21/2014 10:31 AM, Paolo Bonzini wrote:
> Userspace is expecting non-compacted format for KVM_GET_XSAVE, but
> struct xsave_struct might be using the compacted format. Convert
> in order to preserve userspace ABI.
>
> Fixes: f31a9f7c71691569359fa7fb8b0acaa44bce0324
> Cc: Fenghua Yu <fenghua.yu@intel.com>
> Cc: stable@vger.kernel.org
> Cc: Nadav Amit <namit@cs.technion.ac.il>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> arch/x86/kvm/x86.c | 48 +++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 43 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 5337039427c8..7e8a20e5615a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3131,15 +3131,53 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
> return 0;
> }
>
> +#define XSTATE_COMPACTION_ENABLED (1ULL << 63)
> +
> +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 valid;
> +
> + /*
> + * Copy legacy XSAVE area, to avoid complications with CPUID
> + * leaves 0 and 1 in the loop below.
> + */
> + memcpy(dest, xsave, XSAVE_HDR_OFFSET);
> +
> + /* Set XSTATE_BV */
> + *(u64 *)(dest + XSAVE_HDR_OFFSET) = xstate_bv;
> +
> + /*
> + * Copy each region from the possibly compacted offset to the
> + * non-compacted offset.
> + */
> + valid = xstate_bv & ~XSTATE_FPSSE;
> + if (xsave->xsave_hdr.xcomp_bv & XSTATE_COMPACTION_ENABLED)
> + valid &= xsave->xsave_hdr.xcomp_bv;
> +
> + while (valid) {
> + u64 feature = valid & -valid;
> + int index = fls64(feature) - 1;
> + void *src = get_xsave_addr(xsave, feature);
> +
> + if (src) {
> + u32 size, offset, ecx, edx;
> + cpuid_count(XSTATE_CPUID, index,
> + &size, &offset, &ecx, &edx);
> + memcpy(dest + offset, src, size);

Is this really the best way to do this? cpuid is serializing, so this
is possibly *very* slow.

--Andy


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