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KVM: nVMX: Handling of CR0 and CR4 modifying instructions

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When L2 tries to modify CR0 or CR4 (with mov or clts), and modifies a bit
which L1 asked to shadow (via CR[04]_GUEST_HOST_MASK), we already do the right
thing: we let L1 handle the trap (see nested_vmx_exit_handled_cr() in a
previous patch).
When L2 modifies bits that L1 doesn't care about, we let it think (via
CR[04]_READ_SHADOW) that it did these modifications, while only changing
(in GUEST_CR[04]) the bits that L0 doesn't shadow.

This is needed for corect handling of CR0.TS for lazy FPU loading: L0 may
want to leave TS on, while pretending to allow the guest to change it.

Signed-off-by: Nadav Har'El <nyh@il.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Nadav Har'El 2011-05-25 23:14:38 +03:00 committed by Avi Kivity
parent 66c78ae40c
commit eeadf9e755
1 changed files with 55 additions and 3 deletions
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58
arch/x86/kvm/vmx.c
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@ -4164,6 +4164,58 @@ vmx_patch_hypercall(struct kvm_vcpu *vcpu, unsigned char *hypercall)
hypercall[2] = 0xc1;
}
/* called to set cr0 as approriate for a mov-to-cr0 exit. */
static int handle_set_cr0(struct kvm_vcpu *vcpu, unsigned long val)
{
if (to_vmx(vcpu)->nested.vmxon &&
((val & VMXON_CR0_ALWAYSON) != VMXON_CR0_ALWAYSON))
return 1;
if (is_guest_mode(vcpu)) {
/*
* We get here when L2 changed cr0 in a way that did not change
* any of L1's shadowed bits (see nested_vmx_exit_handled_cr),
* but did change L0 shadowed bits. This can currently happen
* with the TS bit: L0 may want to leave TS on (for lazy fpu
* loading) while pretending to allow the guest to change it.
*/
if (kvm_set_cr0(vcpu, (val & vcpu->arch.cr0_guest_owned_bits) |
(vcpu->arch.cr0 & ~vcpu->arch.cr0_guest_owned_bits)))
return 1;
vmcs_writel(CR0_READ_SHADOW, val);
return 0;
} else
return kvm_set_cr0(vcpu, val);
}
static int handle_set_cr4(struct kvm_vcpu *vcpu, unsigned long val)
{
if (is_guest_mode(vcpu)) {
if (kvm_set_cr4(vcpu, (val & vcpu->arch.cr4_guest_owned_bits) |
(vcpu->arch.cr4 & ~vcpu->arch.cr4_guest_owned_bits)))
return 1;
vmcs_writel(CR4_READ_SHADOW, val);
return 0;
} else
return kvm_set_cr4(vcpu, val);
}
/* called to set cr0 as approriate for clts instruction exit. */
static void handle_clts(struct kvm_vcpu *vcpu)
{
if (is_guest_mode(vcpu)) {
/*
* We get here when L2 did CLTS, and L1 didn't shadow CR0.TS
* but we did (!fpu_active). We need to keep GUEST_CR0.TS on,
* just pretend it's off (also in arch.cr0 for fpu_activate).
*/
vmcs_writel(CR0_READ_SHADOW,
vmcs_readl(CR0_READ_SHADOW) & ~X86_CR0_TS);
vcpu->arch.cr0 &= ~X86_CR0_TS;
} else
vmx_set_cr0(vcpu, kvm_read_cr0_bits(vcpu, ~X86_CR0_TS));
}
static int handle_cr(struct kvm_vcpu *vcpu)
{
unsigned long exit_qualification, val;
@ -4180,7 +4232,7 @@ static int handle_cr(struct kvm_vcpu *vcpu)
trace_kvm_cr_write(cr, val);
switch (cr) {
case 0:
err = kvm_set_cr0(vcpu, val);
err = handle_set_cr0(vcpu, val);
kvm_complete_insn_gp(vcpu, err);
return 1;
case 3:
@ -4188,7 +4240,7 @@ static int handle_cr(struct kvm_vcpu *vcpu)
kvm_complete_insn_gp(vcpu, err);
return 1;
case 4:
err = kvm_set_cr4(vcpu, val);
err = handle_set_cr4(vcpu, val);
kvm_complete_insn_gp(vcpu, err);
return 1;
case 8: {
@ -4206,7 +4258,7 @@ static int handle_cr(struct kvm_vcpu *vcpu)
};
break;
case 2: /* clts */
vmx_set_cr0(vcpu, kvm_read_cr0_bits(vcpu, ~X86_CR0_TS));
handle_clts(vcpu);
trace_kvm_cr_write(0, kvm_read_cr0(vcpu));
skip_emulated_instruction(vcpu);
vmx_fpu_activate(vcpu);