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Subject[PATCH 1/2] KVM: x86: introduce kvm_supported_xcr0()
Date
XSAVE support for KVM is already using host_xcr0 & KVM_SUPPORTED_XCR0 as
a "dynamic" version of KVM_SUPPORTED_XCR0.

However, this is not enough because the MPX bits should not be presented
to the guest unless kvm_x86_ops confirms the support. So, replace all
instances of host_xcr0 & KVM_SUPPORTED_XCR0 with a new function
kvm_supported_xcr0() that also has this check.

Note that here:

if (xstate_bv & ~KVM_SUPPORTED_XCR0)
return -EINVAL;
if (xstate_bv & ~host_cr0)
return -EINVAL;

the code is equivalent to

if ((xstate_bv & ~KVM_SUPPORTED_XCR0) ||
(xstate_bv & ~host_cr0)
return -EINVAL;

i.e. "xstate_bv & (~KVM_SUPPORTED_XCR0 | ~host_cr0)" which is in turn
equal to "xstate_bv & ~(KVM_SUPPORTED_XCR0 & host_cr0)". So we should
also use the new function there.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/cpuid.c | 27 ++++++++++++++++-----------
arch/x86/kvm/x86.c | 4 +---
arch/x86/kvm/x86.h | 2 ++
3 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index ddc8a7e165df..18aefb4d0927 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -43,6 +43,16 @@ static u32 xstate_required_size(u64 xstate_bv)
return ret;
}

+u64 kvm_supported_xcr0(void)
+{
+ u64 xcr0 = KVM_SUPPORTED_XCR0 & host_xcr0;
+
+ if (!kvm_x86_ops->mpx_supported || !kvm_x86_ops->mpx_supported())
+ xcr0 &= ~(XSTATE_BNDREGS | XSTATE_BNDCSR);
+
+ return xcr0;
+}
+
void kvm_update_cpuid(struct kvm_vcpu *vcpu)
{
struct kvm_cpuid_entry2 *best;
@@ -73,7 +83,7 @@ void kvm_update_cpuid(struct kvm_vcpu *vcpu)
} else {
vcpu->arch.guest_supported_xcr0 =
(best->eax | ((u64)best->edx << 32)) &
- host_xcr0 & KVM_SUPPORTED_XCR0;
+ kvm_supported_xcr0();
vcpu->arch.guest_xstate_size = best->ebx =
xstate_required_size(vcpu->arch.xcr0);
}
@@ -210,13 +220,6 @@ static void do_cpuid_1_ent(struct kvm_cpuid_entry2 *entry, u32 function,
entry->flags = 0;
}

-static bool supported_xcr0_bit(unsigned bit)
-{
- u64 mask = ((u64)1 << bit);
-
- return mask & KVM_SUPPORTED_XCR0 & host_xcr0;
-}
-
#define F(x) bit(X86_FEATURE_##x)

static int __do_cpuid_ent_emulated(struct kvm_cpuid_entry2 *entry,
@@ -439,16 +442,18 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
}
case 0xd: {
int idx, i;
+ u64 supported = kvm_supported_xcr0();

- entry->eax &= host_xcr0 & KVM_SUPPORTED_XCR0;
- entry->edx &= (host_xcr0 & KVM_SUPPORTED_XCR0) >> 32;
+ entry->eax &= supported;
+ entry->edx &= supported >> 32;
entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
for (idx = 1, i = 1; idx < 64; ++idx) {
+ u64 mask = ((u64)1 << idx);
if (*nent >= maxnent)
goto out;

do_cpuid_1_ent(&entry[i], function, idx);
- if (entry[i].eax == 0 || !supported_xcr0_bit(idx))
+ if (entry[i].eax == 0 || !(supported & mask))
continue;
entry[i].flags |=
KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6530019116b0..4e038cda45a2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3048,9 +3048,7 @@ static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu,
* CPUID leaf 0xD, index 0, EDX:EAX. This is for compatibility
* with old userspace.
*/
- if (xstate_bv & ~KVM_SUPPORTED_XCR0)
- return -EINVAL;
- if (xstate_bv & ~host_xcr0)
+ if (xstate_bv & ~kvm_supported_xcr0())
return -EINVAL;
memcpy(&vcpu->arch.guest_fpu.state->xsave,
guest_xsave->region, vcpu->arch.guest_xstate_size);
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 392ecbff0030..8c97bac9a895 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -126,6 +126,8 @@ int kvm_write_guest_virt_system(struct x86_emulate_ctxt *ctxt,
| XSTATE_BNDREGS | XSTATE_BNDCSR)
extern u64 host_xcr0;

+extern u64 kvm_supported_xcr0(void);
+
extern unsigned int min_timer_period_us;

extern struct static_key kvm_no_apic_vcpu;
--
1.8.3.1



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