[RFC PATCH v2 2/3] KVM: arm64: set FnV in vcpu's ESR_ELx when host FAR_EL2 is invalid

[Jiaqi Yan <jiaqiyan@google.com>]

Certain microarchitectures (e.g. Neoverse V2) do not keep track of
the faulting address for a memory load that consumes poisoned data
and results in a synchronous external abort (SEA). This means the
poisoned guest physical address is unavailable when KVM handles such
SEA in EL2, and FAR_EL2 just holds a garbage value. KVM sends SIGBUS
to interrupt VMM/vCPU but the si_addr will be zero.

In case VMM later asks KVM to synchronously inject a SEA into the
guest, KVM should set FnV bit
- in vcpu's ESR_EL1 to let guest kernel know that FAR_EL1
- in vcpu's ESR_EL2 to let nested virtualization know that FAR_EL2
is also invalid and holds garbage value.

Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
---
 arch/arm64/kvm/inject_fault.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm64/kvm/inject_fault.c b/arch/arm64/kvm/inject_fault.c
index a640e839848e6..2b01b331a4879 100644
--- a/arch/arm64/kvm/inject_fault.c
+++ b/arch/arm64/kvm/inject_fault.c
@@ -13,6 +13,7 @@
 #include <linux/kvm_host.h>
 #include <asm/kvm_emulate.h>
 #include <asm/kvm_nested.h>
+#include <asm/kvm_ras.h>
 #include <asm/esr.h>
 
 static void pend_sync_exception(struct kvm_vcpu *vcpu)
@@ -81,6 +82,9 @@ static void inject_abt64(struct kvm_vcpu *vcpu, bool is_iabt, unsigned long addr
 	if (!is_iabt)
 		esr |= ESR_ELx_EC_DABT_LOW << ESR_ELx_EC_SHIFT;
 
+	if (!kvm_vcpu_sea_far_valid(vcpu))
+		esr |= ESR_ELx_FnV;
+
 	esr |= ESR_ELx_FSC_EXTABT;
 
 	if (match_target_el(vcpu, unpack_vcpu_flag(EXCEPT_AA64_EL1_SYNC))) {
-- 
2.47.0.338.g60cca15819-goog