[PATCH v2 1/6] KVM: x86: Add dedicated storage for guest RIP

Sean Christopherson
2026-04-09T22:42:49Z

Add kvm_vcpu_arch.rip to track guest RIP instead of including it in the
generic regs[] array. Decoupling RIP from regs[] will allow using a
*completely* arbitrary index for RIP, as opposed to the mostly-arbitrary
index that is currently used. That in turn will allow using indices
16-31 to track R16-R31 that are coming with APX.

Note, although RIP can used for addressing, it does NOT have an
architecturally defined index, and so can't be reached via flows like
get_vmx_mem_address() where KVM "blindly" reads a general purpose register
given the SIB information reported by hardware. For RIP-relative
addressing, hardware reports the full "offset" in vmcs.EXIT_QUALIFICATION.

Note #2, keep the available/dirty tracking as RSP is context switched
through the VMCS, i.e. needs to be cached for VMX.

Opportunistically rename NR_VCPU_REGS to NR_VCPU_GENERAL_PURPOSE_REGS to
better capture what it tracks, and so that KVM can slot in R16-R13 without
running into weirdness where KVM's definition of "EXREG" doesn't line up
with APX's definition of "extended reg".

No functional change intended.

Cc: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/include/asm/kvm_host.h | 10 ++++++----
arch/x86/kvm/kvm_cache_regs.h | 12 ++++++++----
arch/x86/kvm/svm/sev.c | 2 +-
arch/x86/kvm/svm/svm.c | 6 +++---
arch/x86/kvm/vmx/vmx.c | 8 ++++----
arch/x86/kvm/vmx/vmx.h | 2 +-
6 files changed, 23 insertions(+), 17 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index c470e40a00aa..68a11325e8bc 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -191,10 +191,11 @@ enum kvm_reg {
VCPU_REGS_R14 = __VCPU_REGS_R14,
VCPU_REGS_R15 = __VCPU_REGS_R15,
#endif
- VCPU_REGS_RIP,
- NR_VCPU_REGS,
+ NR_VCPU_GENERAL_PURPOSE_REGS,

- VCPU_EXREG_PDPTR = NR_VCPU_REGS,
+ VCPU_REG_RIP = NR_VCPU_GENERAL_PURPOSE_REGS,
+
+ VCPU_EXREG_PDPTR,
VCPU_EXREG_CR0,
/*
* Alias AMD's ERAPS (not a real register) to CR3 so that common code
@@ -799,7 +800,8 @@ struct kvm_vcpu_arch {
* rip and regs accesses must go through
* kvm_{register,rip}_{read,write} functions.
*/
- unsigned long regs[NR_VCPU_REGS];
+ unsigned long regs[NR_VCPU_GENERAL_PURPOSE_REGS];
+ unsigned long rip;
u32 regs_avail;
u32 regs_dirty;

diff --git a/arch/x86/kvm/kvm_cache_regs.h b/arch/x86/kvm/kvm_cache_regs.h
index 8ddb01191d6f..9b7df9de0e87 100644
--- a/arch/x86/kvm/kvm_cache_regs.h
+++ b/arch/x86/kvm/kvm_cache_regs.h
@@ -112,7 +112,7 @@ static __always_inline bool kvm_register_test_and_mark_available(struct kvm_vcpu
*/
static inline unsigned long kvm_register_read_raw(struct kvm_vcpu *vcpu, int reg)
{
- if (WARN_ON_ONCE((unsigned int)reg >= NR_VCPU_REGS))
+ if (WARN_ON_ONCE((unsigned int)reg >= NR_VCPU_GENERAL_PURPOSE_REGS))
return 0;

if (!kvm_register_is_available(vcpu, reg))
@@ -124,7 +124,7 @@ static inline unsigned long kvm_register_read_raw(struct kvm_vcpu *vcpu, int reg
static inline void kvm_register_write_raw(struct kvm_vcpu *vcpu, int reg,
unsigned long val)
{
- if (WARN_ON_ONCE((unsigned int)reg >= NR_VCPU_REGS))
+ if (WARN_ON_ONCE((unsigned int)reg >= NR_VCPU_GENERAL_PURPOSE_REGS))
return;

vcpu->arch.regs[reg] = val;
@@ -133,12 +133,16 @@ static inline void kvm_register_write_raw(struct kvm_vcpu *vcpu, int reg,

static inline unsigned long kvm_rip_read(struct kvm_vcpu *vcpu)
{
- return kvm_register_read_raw(vcpu, VCPU_REGS_RIP);
+ if (!kvm_register_is_available(vcpu, VCPU_REG_RIP))
+ kvm_x86_call(cache_reg)(vcpu, VCPU_REG_RIP);
+
+ return vcpu->arch.rip;
}

static inline void kvm_rip_write(struct kvm_vcpu *vcpu, unsigned long val)
{
- kvm_register_write_raw(vcpu, VCPU_REGS_RIP, val);
+ vcpu->arch.rip = val;
+ kvm_register_mark_dirty(vcpu, VCPU_REG_RIP);
}

static inline unsigned long kvm_rsp_read(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 75d0c03d69bc..2010b157e288 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -967,7 +967,7 @@ static int sev_es_sync_vmsa(struct vcpu_svm *svm)
save->r14 = svm->vcpu.arch.regs[VCPU_REGS_R14];
save->r15 = svm->vcpu.arch.regs[VCPU_REGS_R15];
#endif
- save->rip = svm->vcpu.arch.regs[VCPU_REGS_RIP];
+ save->rip = svm->vcpu.arch.rip;

/* Sync some non-GPR registers before encrypting */
save->xcr0 = svm->vcpu.arch.xcr0;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index e7fdd7a9c280..85edaee27b03 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4420,7 +4420,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags)

svm->vmcb->save.rax = vcpu->arch.regs[VCPU_REGS_RAX];
svm->vmcb->save.rsp = vcpu->arch.regs[VCPU_REGS_RSP];
- svm->vmcb->save.rip = vcpu->arch.regs[VCPU_REGS_RIP];
+ svm->vmcb->save.rip = vcpu->arch.rip;

/*
* Disable singlestep if we're injecting an interrupt/exception.
@@ -4506,7 +4506,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags)
vcpu->arch.cr2 = svm->vmcb->save.cr2;
vcpu->arch.regs[VCPU_REGS_RAX] = svm->vmcb->save.rax;
vcpu->arch.regs[VCPU_REGS_RSP] = svm->vmcb->save.rsp;
- vcpu->arch.regs[VCPU_REGS_RIP] = svm->vmcb->save.rip;
+ vcpu->arch.rip = svm->vmcb->save.rip;
}
vcpu->arch.regs_dirty = 0;

@@ -4946,7 +4946,7 @@ static int svm_enter_smm(struct kvm_vcpu *vcpu, union kvm_smram *smram)

svm->vmcb->save.rax = vcpu->arch.regs[VCPU_REGS_RAX];
svm->vmcb->save.rsp = vcpu->arch.regs[VCPU_REGS_RSP];
- svm->vmcb->save.rip = vcpu->arch.regs[VCPU_REGS_RIP];
+ svm->vmcb->save.rip = vcpu->arch.rip;

nested_svm_simple_vmexit(svm, SVM_EXIT_SW);

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index a29896a9ef14..577b0c6286ad 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2604,8 +2604,8 @@ void vmx_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)
case VCPU_REGS_RSP:
vcpu->arch.regs[VCPU_REGS_RSP] = vmcs_readl(GUEST_RSP);
break;
- case VCPU_REGS_RIP:
- vcpu->arch.regs[VCPU_REGS_RIP] = vmcs_readl(GUEST_RIP);
+ case VCPU_REG_RIP:
+ vcpu->arch.rip = vmcs_readl(GUEST_RIP);
break;
case VCPU_EXREG_PDPTR:
if (enable_ept)
@@ -7536,8 +7536,8 @@ fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags)

if (kvm_register_is_dirty(vcpu, VCPU_REGS_RSP))
vmcs_writel(GUEST_RSP, vcpu->arch.regs[VCPU_REGS_RSP]);
- if (kvm_register_is_dirty(vcpu, VCPU_REGS_RIP))
- vmcs_writel(GUEST_RIP, vcpu->arch.regs[VCPU_REGS_RIP]);
+ if (kvm_register_is_dirty(vcpu, VCPU_REG_RIP))
+ vmcs_writel(GUEST_RIP, vcpu->arch.rip);
vcpu->arch.regs_dirty = 0;

if (run_flags & KVM_RUN_LOAD_GUEST_DR6)
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index db84e8001da5..d0cc5f6c6879 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -620,7 +620,7 @@ BUILD_CONTROLS_SHADOW(tertiary_exec, TERTIARY_VM_EXEC_CONTROL, 64)
* cache on demand. Other registers not listed here are synced to
* the cache immediately after VM-Exit.
*/
-#define VMX_REGS_LAZY_LOAD_SET ((1 << VCPU_REGS_RIP) | \
+#define VMX_REGS_LAZY_LOAD_SET ((1 << VCPU_REG_RIP) | \
(1 << VCPU_REGS_RSP) | \
(1 << VCPU_EXREG_RFLAGS) | \
(1 << VCPU_EXREG_PDPTR) | \
--
2.53.0.1213.gd9a14994de-goog