KVM's "Lazy FPU loading" means that sometimes L0 needs to set CR0.TS, even
if a guest didn't set it. Moreover, L0 must also trap CR0.TS changes and
NM exceptions, even if we have a guest hypervisor (L1) who didn't want these
traps. And of course, conversely: If L1 wanted to trap these events, we
must let it, even if L0 is not interested in them.
This patch fixes some existing KVM code (in update_exception_bitmap(),
vmx_fpu_activate(), vmx_fpu_deactivate()) to do the correct merging of L0's
and L1's needs. Note that handle_cr() was already fixed in the above patch,
and that new code in introduced in previous patches already handles CR0
correctly (see prepare_vmcs02(), prepare_vmcs12(), and nested_vmx_vmexit()).
Signed-off-by: Nadav Har'El <nyh@xxxxxxxxxx>
---
arch/x86/kvm/vmx.c | 38 +++++++++++++++++++++++++++++++++++---
1 file changed, 35 insertions(+), 3 deletions(-)
--- .before/arch/x86/kvm/vmx.c 2011-01-26 18:06:06.000000000 +0200
+++ .after/arch/x86/kvm/vmx.c 2011-01-26 18:06:06.000000000 +0200
@@ -1101,6 +1101,15 @@ static void update_exception_bitmap(stru
eb &= ~(1u << PF_VECTOR); /* bypass_guest_pf = 0 */
if (vcpu->fpu_active)
eb &= ~(1u << NM_VECTOR);
+
+ /* When we are running a nested L2 guest and L1 specified for it a
+ * certain exception bitmap, we must trap the same exceptions and pass
+ * them to L1. When running L2, we will only handle the exceptions
+ * specified above if L1 did not want them.
+ */
+ if (is_guest_mode(vcpu))
+ eb |= get_vmcs12_fields(vcpu)->exception_bitmap;
+
vmcs_write32(EXCEPTION_BITMAP, eb);
}
@@ -1393,8 +1402,19 @@ static void vmx_fpu_activate(struct kvm_
cr0 &= ~(X86_CR0_TS | X86_CR0_MP);
cr0 |= kvm_read_cr0_bits(vcpu, X86_CR0_TS | X86_CR0_MP);
vmcs_writel(GUEST_CR0, cr0);
- update_exception_bitmap(vcpu);
vcpu->arch.cr0_guest_owned_bits = X86_CR0_TS;
+ if (is_guest_mode(vcpu)) {
+ /* While we (L0) no longer care about NM exceptions or cr0.TS
+ * changes, our guest hypervisor (L1) might care in which case
+ * we must trap them for it.
+ */
+ u32 eb = vmcs_read32(EXCEPTION_BITMAP) & ~(1u << NM_VECTOR);
+ struct vmcs_fields *vmcs12 = get_vmcs12_fields(vcpu);
+ eb |= vmcs12->exception_bitmap;
+ vcpu->arch.cr0_guest_owned_bits &= ~vmcs12->cr0_guest_host_mask;
+ vmcs_write32(EXCEPTION_BITMAP, eb);
+ } else
+ update_exception_bitmap(vcpu);
vmcs_writel(CR0_GUEST_HOST_MASK, ~vcpu->arch.cr0_guest_owned_bits);
}
@@ -1402,12 +1422,24 @@ static void vmx_decache_cr0_guest_bits(s
static void vmx_fpu_deactivate(struct kvm_vcpu *vcpu)
{
+ /* Note that there is no vcpu->fpu_active = 0 here. The caller must
+ * set this *before* calling this function.
+ */
vmx_decache_cr0_guest_bits(vcpu);
vmcs_set_bits(GUEST_CR0, X86_CR0_TS | X86_CR0_MP);
- update_exception_bitmap(vcpu);
+ vmcs_write32(EXCEPTION_BITMAP,
+ vmcs_read32(EXCEPTION_BITMAP) | (1u << NM_VECTOR));
vcpu->arch.cr0_guest_owned_bits = 0;
vmcs_writel(CR0_GUEST_HOST_MASK, ~vcpu->arch.cr0_guest_owned_bits);
- vmcs_writel(CR0_READ_SHADOW, vcpu->arch.cr0);
+ if (is_guest_mode(vcpu))
+ /* Unfortunately in nested mode we play with arch.cr0's PG
+ * bit, so we musn't copy it all, just the relevant TS bit
+ */
+ vmcs_writel(CR0_READ_SHADOW,
+ (vmcs_readl(CR0_READ_SHADOW) & ~X86_CR0_TS) |
+ (vcpu->arch.cr0 & X86_CR0_TS));
+ else
+ vmcs_writel(CR0_READ_SHADOW, vcpu->arch.cr0);
}
static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
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