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KVM: x86: Allow force_emulation_prefix to be written without a reload

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Allow force_emulation_prefix to be written by privileged userspace
without reloading KVM.  The param does not have any persistent affects
and is trivial to snapshot.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220830231614.3580124-28-seanjc@google.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2022-08-30 23:16:14 +00:00 • committed by Paolo Bonzini
parent 28c40b2cfb
commit 40aaa5b6da
1 changed files with 4 additions and 3 deletions
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7
arch/x86/kvm/x86.c
View file

@ -179,7 +179,7 @@ EXPORT_SYMBOL_GPL(enable_vmware_backdoor);
*/
#define KVM_FEP_CLEAR_RFLAGS_RF BIT(1)
static int __read_mostly force_emulation_prefix;
module_param(force_emulation_prefix, int, 0444);
module_param(force_emulation_prefix, int, 0644);
int __read_mostly pi_inject_timer = -1;
module_param(pi_inject_timer, bint, S_IRUGO | S_IWUSR);
@ -7287,6 +7287,7 @@ static int kvm_can_emulate_insn(struct kvm_vcpu *vcpu, int emul_type,
int handle_ud(struct kvm_vcpu *vcpu)
{
static const char kvm_emulate_prefix[] = { __KVM_EMULATE_PREFIX };
int fep_flags = READ_ONCE(force_emulation_prefix);
int emul_type = EMULTYPE_TRAP_UD;
char sig[5]; /* ud2; .ascii "kvm" */
struct x86_exception e;
@ -7294,11 +7295,11 @@ int handle_ud(struct kvm_vcpu *vcpu)
if (unlikely(!kvm_can_emulate_insn(vcpu, emul_type, NULL, 0)))
return 1;
if (force_emulation_prefix &&
if (fep_flags &&
kvm_read_guest_virt(vcpu, kvm_get_linear_rip(vcpu),
sig, sizeof(sig), &e) == 0 &&
memcmp(sig, kvm_emulate_prefix, sizeof(sig)) == 0) {
if (force_emulation_prefix & KVM_FEP_CLEAR_RFLAGS_RF)
if (fep_flags & KVM_FEP_CLEAR_RFLAGS_RF)
kvm_set_rflags(vcpu, kvm_get_rflags(vcpu) & ~X86_EFLAGS_RF);
kvm_rip_write(vcpu, kvm_rip_read(vcpu) + sizeof(sig));
emul_type = EMULTYPE_TRAP_UD_FORCED;