[PATCH 2/9] KVM: x86: support XSAVES usage in the host

Paolo Bonzini
2014-12-04T15:57:07Z

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.

Likewise, userspace is passing non-compacted format for KVM_SET_XSAVE
but the kernel will pass it to XRSTORS, and we need to convert back.

Fixes: f31a9f7c71691569359fa7fb8b0acaa44bce0324
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: stable@vger.kernel.org
Cc: H. Peter Anvin <hpa@linux.intel.com>
Reported-by: Nadav Amit <namit@cs.technion.ac.il>
Tested-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/x86.c | 90 +++++++++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 83 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 08b5657e57ed..c259814200bd 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3132,15 +3132,89 @@ 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 = xsave->xsave_hdr.xstate_bv;
+ 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;
+ 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);
+ }
+
+ valid -= feature;
+ }
+}
+
+static void load_xsave(struct kvm_vcpu *vcpu, u8 *src)
+{
+ struct xsave_struct *xsave = &vcpu->arch.guest_fpu.state->xsave;
+ u64 xstate_bv = *(u64 *)(src + XSAVE_HDR_OFFSET);
+ u64 valid;
+
+ /*
+ * Copy legacy XSAVE area, to avoid complications with CPUID
+ * leaves 0 and 1 in the loop below.
+ */
+ memcpy(xsave, src, XSAVE_HDR_OFFSET);
+
+ /* Set XSTATE_BV and possibly XCOMP_BV. */
+ xsave->xsave_hdr.xstate_bv = xstate_bv;
+ if (cpu_has_xsaves)
+ xsave->xsave_hdr.xcomp_bv = host_xcr0 | XSTATE_COMPACTION_ENABLED;
+
+ /*
+ * Copy each region from the non-compacted offset to the
+ * possibly compacted offset.
+ */
+ valid = xstate_bv & ~XSTATE_FPSSE;
+ while (valid) {
+ u64 feature = valid & -valid;
+ int index = fls64(feature) - 1;
+ void *dest = get_xsave_addr(xsave, feature);
+
+ if (dest) {
+ u32 size, offset, ecx, edx;
+ cpuid_count(XSTATE_CPUID, index,
+ &size, &offset, &ecx, &edx);
+ memcpy(dest, src + offset, size);
+ } else
+ WARN_ON_ONCE(1);
+
+ valid -= feature;
+ }
+}
+
static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu,
struct kvm_xsave *guest_xsave)
{
if (cpu_has_xsave) {
- memcpy(guest_xsave->region,
- &vcpu->arch.guest_fpu.state->xsave,
- vcpu->arch.guest_xstate_size);
- *(u64 *)&guest_xsave->region[XSAVE_HDR_OFFSET / sizeof(u32)] &=
- vcpu->arch.guest_supported_xcr0 | XSTATE_FPSSE;
+ memset(guest_xsave, 0, sizeof(struct kvm_xsave));
+ fill_xsave((u8 *) guest_xsave->region, vcpu);
} else {
memcpy(guest_xsave->region,
&vcpu->arch.guest_fpu.state->fxsave,
@@ -3164,8 +3238,7 @@ static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu,
*/
if (xstate_bv & ~kvm_supported_xcr0())
return -EINVAL;
- memcpy(&vcpu->arch.guest_fpu.state->xsave,
- guest_xsave->region, vcpu->arch.guest_xstate_size);
+ load_xsave(vcpu, (u8 *)guest_xsave->region);
} else {
if (xstate_bv & ~XSTATE_FPSSE)
return -EINVAL;
@@ -6882,6 +6955,9 @@ int fx_init(struct kvm_vcpu *vcpu)
return err;

fpu_finit(&vcpu->arch.guest_fpu);
+ if (cpu_has_xsaves)
+ vcpu->arch.guest_fpu.state->xsave.xsave_hdr.xcomp_bv =
+ host_xcr0 | XSTATE_COMPACTION_ENABLED;

/*
* Ensure guest xcr0 is valid for loading
--
1.8.3.1