[PATCH v6 5/9] KVM: x86: Add support for vICR APIC-write VM-Exits in x2APIC mode

Zeng Guang
2022-02-25T08:53:45Z

Upcoming Intel CPUs will support virtual x2APIC MSR writes to the vICR,
i.e. will trap and generate an APIC-write VM-Exit instead of intercepting
the WRMSR. Add support for handling "nodecode" x2APIC writes, which
were previously impossible.

Note, x2APIC MSR writes are 64 bits wide.

Signed-off-by: Zeng Guang <guang.zeng@intel.com>
---
arch/x86/kvm/lapic.c | 25 ++++++++++++++++++++++---
1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 629c116b0d3e..e4bcdab1fac0 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -67,6 +67,7 @@ static bool lapic_timer_advance_dynamic __read_mostly;
#define LAPIC_TIMER_ADVANCE_NS_MAX 5000
/* step-by-step approximation to mitigate fluctuation */
#define LAPIC_TIMER_ADVANCE_ADJUST_STEP 8
+static int kvm_lapic_msr_read(struct kvm_lapic *apic, u32 reg, u64 *data);

static inline void __kvm_lapic_set_reg(char *regs, int reg_off, u32 val)
{
@@ -2227,10 +2228,28 @@ EXPORT_SYMBOL_GPL(kvm_lapic_set_eoi);
/* emulate APIC access in a trap manner */
void kvm_apic_write_nodecode(struct kvm_vcpu *vcpu, u32 offset)
{
- u32 val = kvm_lapic_get_reg(vcpu->arch.apic, offset);
+ struct kvm_lapic *apic = vcpu->arch.apic;
+ u64 val;
+
+ if (apic_x2apic_mode(apic)) {
+ /*
+ * When guest APIC is in x2APIC mode and IPI virtualization
+ * is enabled, accessing APIC_ICR may cause trap-like VM-exit
+ * on Intel hardware. Other offsets are not possible.
+ */
+ if (WARN_ON_ONCE(offset != APIC_ICR))
+ return;

- /* TODO: optimize to just emulate side effect w/o one more write */
- kvm_lapic_reg_write(vcpu->arch.apic, offset, val);
+ kvm_lapic_msr_read(apic, offset, &val);
+ if (val & APIC_ICR_BUSY)
+ kvm_x2apic_icr_write(apic, val);
+ else
+ kvm_apic_send_ipi(apic, (u32)val, (u32)(val >> 32));
+ } else {
+ val = kvm_lapic_get_reg(apic, offset);
+ /* TODO: optimize to just emulate side effect w/o one more write */
+ kvm_lapic_reg_write(apic, offset, (u32)val);
+ }
}
EXPORT_SYMBOL_GPL(kvm_apic_write_nodecode);

--
2.27.0