From 40aaa5b6dadc2cbdfff004c31fdd00b9684ff1a8 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@google.com>
Date: Tue, 30 Aug 2022 23:16:14 +0000
Subject: [PATCH] KVM: x86: Allow force_emulation_prefix to be written without
a reload
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>
---
arch/x86/kvm/x86.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c0d5d512edfa2..a532b9dea57b4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -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;
--
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