[PATCH v6 41/44] KVM: VMX: Compartmentalize adding MSRs to host vs. guest auto-load list

Sean Christopherson
2025-12-06T00:18:50Z

Undo the bundling of the "host" and "guest" MSR auto-load list logic so
that the code can be deduplicated by factoring out the logic to a separate
helper. Now that "list full" situations are treated as fatal to the VM,
there is no need to pre-check both lists.

For all intents and purposes, this reverts the add_atomic_switch_msr()
changes made by commit 3190709335dd ("x86/KVM/VMX: Separate the VMX
AUTOLOAD guest/host number accounting").

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/vmx/vmx.c | 23 ++++++++++++-----------
1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index be2a2580e8f1..018e01daab68 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1096,9 +1096,9 @@ static __always_inline void add_atomic_switch_msr_special(struct vcpu_vmx *vmx,
static void add_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr,
u64 guest_val, u64 host_val)
{
- int i, j = 0;
struct msr_autoload *m = &vmx->msr_autoload;
struct kvm *kvm = vmx->vcpu.kvm;
+ int i;

switch (msr) {
case MSR_EFER:
@@ -1133,25 +1133,26 @@ static void add_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr,
}

i = vmx_find_loadstore_msr_slot(&m->guest, msr);
- j = vmx_find_loadstore_msr_slot(&m->host, msr);
-
- if (KVM_BUG_ON(i < 0 && m->guest.nr == MAX_NR_LOADSTORE_MSRS, kvm) ||
- KVM_BUG_ON(j < 0 && m->host.nr == MAX_NR_LOADSTORE_MSRS, kvm))
- return;
-
if (i < 0) {
+ if (KVM_BUG_ON(m->guest.nr == MAX_NR_LOADSTORE_MSRS, kvm))
+ return;
+
i = m->guest.nr++;
m->guest.val[i].index = msr;
vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, m->guest.nr);
}
m->guest.val[i].value = guest_val;

- if (j < 0) {
- j = m->host.nr++;
- m->host.val[j].index = msr;
+ i = vmx_find_loadstore_msr_slot(&m->host, msr);
+ if (i < 0) {
+ if (KVM_BUG_ON(m->host.nr == MAX_NR_LOADSTORE_MSRS, kvm))
+ return;
+
+ i = m->host.nr++;
+ m->host.val[i].index = msr;
vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, m->host.nr);
}
- m->host.val[j].value = host_val;
+ m->host.val[i].value = host_val;
}

static bool update_transition_efer(struct vcpu_vmx *vmx)
--
2.52.0.223.gf5cc29aaa4-goog