[PATCH 14/14] KVM: x86: Add helpers to prepare kvm_run for userspace MMIO exit
From: Sean Christopherson
Date: Tue Feb 24 2026 - 20:23:39 EST
Add helpers to fill kvm_run for userspace MMIO exits to deduplicate a
variety of code, and to allow for a cleaner return path in
emulator_read_write().
No functional change intended.
Cc: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Cc: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
Cc: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: Michael Roth <michael.roth@xxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/vmx/tdx.c | 14 ++++----------
arch/x86/kvm/x86.c | 42 ++++++++----------------------------------
arch/x86/kvm/x86.h | 24 ++++++++++++++++++++++++
3 files changed, 36 insertions(+), 44 deletions(-)
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 5df9d32d2058..a813c502336c 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1467,17 +1467,11 @@ static int tdx_emulate_mmio(struct kvm_vcpu *vcpu)
/* Request the device emulation to userspace device model. */
vcpu->mmio_is_write = write;
- if (!write)
+
+ __kvm_prepare_emulated_mmio_exit(vcpu, gpa, size, &val, write);
+
+ if (!write) {
vcpu->arch.complete_userspace_io = tdx_complete_mmio_read;
-
- vcpu->run->mmio.phys_addr = gpa;
- vcpu->run->mmio.len = size;
- vcpu->run->mmio.is_write = write;
- vcpu->run->exit_reason = KVM_EXIT_MMIO;
-
- if (write) {
- memcpy(vcpu->run->mmio.data, &val, size);
- } else {
vcpu->mmio_fragments[0].gpa = gpa;
vcpu->mmio_fragments[0].len = size;
trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, size, gpa, NULL);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5376b370b4db..889a9098403c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8210,7 +8210,6 @@ static int emulator_read_write(struct x86_emulate_ctxt *ctxt,
const struct read_write_emulator_ops *ops)
{
struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
- struct kvm_mmio_fragment *frag;
int rc;
if (WARN_ON_ONCE((bytes > 8u || !ops->write) && object_is_on_stack(val)))
@@ -8268,12 +8267,9 @@ static int emulator_read_write(struct x86_emulate_ctxt *ctxt,
vcpu->mmio_needed = 1;
vcpu->mmio_cur_fragment = 0;
+ vcpu->mmio_is_write = ops->write;
- frag = &vcpu->mmio_fragments[0];
- vcpu->run->mmio.len = min(8u, frag->len);
- vcpu->run->mmio.is_write = vcpu->mmio_is_write = ops->write;
- vcpu->run->exit_reason = KVM_EXIT_MMIO;
- vcpu->run->mmio.phys_addr = frag->gpa;
+ kvm_prepare_emulated_mmio_exit(vcpu, &vcpu->mmio_fragments[0]);
/*
* For MMIO reads, stop emulating and immediately exit to userspace, as
@@ -8283,11 +8279,7 @@ static int emulator_read_write(struct x86_emulate_ctxt *ctxt,
* after completing emulation (see the check on vcpu->mmio_needed in
* x86_emulate_instruction()).
*/
- if (!ops->write)
- return X86EMUL_IO_NEEDED;
-
- memcpy(vcpu->run->mmio.data, frag->data, min(8u, frag->len));
- return X86EMUL_CONTINUE;
+ return ops->write ? X86EMUL_CONTINUE : X86EMUL_IO_NEEDED;
}
static int emulator_read_emulated(struct x86_emulate_ctxt *ctxt,
@@ -11884,12 +11876,7 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
return complete_emulated_io(vcpu);
}
- run->exit_reason = KVM_EXIT_MMIO;
- run->mmio.phys_addr = frag->gpa;
- if (vcpu->mmio_is_write)
- memcpy(run->mmio.data, frag->data, min(8u, frag->len));
- run->mmio.len = min(8u, frag->len);
- run->mmio.is_write = vcpu->mmio_is_write;
+ kvm_prepare_emulated_mmio_exit(vcpu, frag);
vcpu->arch.complete_userspace_io = complete_emulated_mmio;
return 0;
}
@@ -14296,15 +14283,8 @@ static int complete_sev_es_emulated_mmio(struct kvm_vcpu *vcpu)
}
// More MMIO is needed
- run->mmio.phys_addr = frag->gpa;
- run->mmio.len = min(8u, frag->len);
- run->mmio.is_write = vcpu->mmio_is_write;
- if (run->mmio.is_write)
- memcpy(run->mmio.data, frag->data, min(8u, frag->len));
- run->exit_reason = KVM_EXIT_MMIO;
-
+ kvm_prepare_emulated_mmio_exit(vcpu, frag);
vcpu->arch.complete_userspace_io = complete_sev_es_emulated_mmio;
-
return 0;
}
@@ -14333,23 +14313,17 @@ int kvm_sev_es_mmio(struct kvm_vcpu *vcpu, bool is_write, gpa_t gpa,
* requests that split a page boundary.
*/
frag = vcpu->mmio_fragments;
- vcpu->mmio_nr_fragments = 1;
frag->len = bytes;
frag->gpa = gpa;
frag->data = data;
vcpu->mmio_needed = 1;
vcpu->mmio_cur_fragment = 0;
+ vcpu->mmio_nr_fragments = 1;
+ vcpu->mmio_is_write = is_write;
- vcpu->run->mmio.phys_addr = gpa;
- vcpu->run->mmio.len = min(8u, frag->len);
- vcpu->run->mmio.is_write = is_write;
- if (is_write)
- memcpy(vcpu->run->mmio.data, frag->data, min(8u, frag->len));
- vcpu->run->exit_reason = KVM_EXIT_MMIO;
-
+ kvm_prepare_emulated_mmio_exit(vcpu, frag);
vcpu->arch.complete_userspace_io = complete_sev_es_emulated_mmio;
-
return 0;
}
EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_sev_es_mmio);
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 1d0f0edd31b3..d66f1c53d2b5 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -718,6 +718,30 @@ int kvm_sev_es_string_io(struct kvm_vcpu *vcpu, unsigned int size,
unsigned int port, void *data, unsigned int count,
int in);
+static inline void __kvm_prepare_emulated_mmio_exit(struct kvm_vcpu *vcpu,
+ gpa_t gpa, unsigned int len,
+ const void *data,
+ bool is_write)
+{
+ struct kvm_run *run = vcpu->run;
+
+ run->mmio.len = min(8u, len);
+ run->mmio.is_write = is_write;
+ run->exit_reason = KVM_EXIT_MMIO;
+ run->mmio.phys_addr = gpa;
+ if (is_write)
+ memcpy(run->mmio.data, data, min(8u, len));
+}
+
+static inline void kvm_prepare_emulated_mmio_exit(struct kvm_vcpu *vcpu,
+ struct kvm_mmio_fragment *frag)
+{
+ WARN_ON_ONCE(!vcpu->mmio_needed || !vcpu->mmio_nr_fragments);
+
+ __kvm_prepare_emulated_mmio_exit(vcpu, frag->gpa, frag->len, frag->data,
+ vcpu->mmio_is_write);
+}
+
static inline bool user_exit_on_hypercall(struct kvm *kvm, unsigned long hc_nr)
{
return kvm->arch.hypercall_exit_enabled & BIT(hc_nr);
--
2.53.0.414.gf7e9f6c205-goog