linux-kernel - [RFC PATCH v2 2/3] KVM: arm64: set FnV in vcpu's ESR_ELx when host FAR

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Message-ID: <20241206010246.40282-2-jiaqiyan@google.com>
Date: Fri,  6 Dec 2024 01:02:45 +0000
From: Jiaqi Yan <jiaqiyan@...gle.com>
To: maz@...nel.org, oliver.upton@...ux.dev
Cc: joey.gouly@....com, suzuki.poulose@....com, yuzenghui@...wei.com, 
	catalin.marinas@....com, will@...nel.org, pbonzini@...hat.com, corbet@....net, 
	kvm@...r.kernel.org, kvmarm@...ts.linux.dev, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	linux-doc@...r.kernel.org, duenwen@...gle.com, rananta@...gle.com, 
	jthoughton@...gle.com, Jiaqi Yan <jiaqiyan@...gle.com>
Subject: [RFC PATCH v2 2/3] KVM: arm64: set FnV in vcpu's ESR_ELx when host
 FAR_EL2 is invalid

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@...gle.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