The patch below does not apply to the 6.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.15.y git checkout FETCH_HEAD git cherry-pick -x c6e35dff58d348c1a9489e9b3b62b3721e62631d # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025081248-omission-talisman-0619@gregkh' --subject-prefix 'PATCH 6.15.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From c6e35dff58d348c1a9489e9b3b62b3721e62631d Mon Sep 17 00:00:00 2001 From: Marc Zyngier maz@kernel.org Date: Sun, 20 Jul 2025 11:22:29 +0100 Subject: [PATCH] KVM: arm64: Check for SYSREGS_ON_CPU before accessing the CPU state
Mark Brown reports that since we commit to making exceptions visible without the vcpu being loaded, the external abort selftest fails.
Upon investigation, it turns out that the code that makes registers affected by an exception visible to the guest is completely broken on VHE, as we don't check whether the system registers are loaded on the CPU at this point. We managed to get away with this so far, but that's obviously as bad as it gets,
Add the required checksm and document the absolute need to check for the SYSREGS_ON_CPU flag before calling into any of the __vcpu_write_sys_reg_to_cpu()__vcpu_read_sys_reg_from_cpu() helpers.
Reported-by: Mark Brown broonie@kernel.org Signed-off-by: Marc Zyngier maz@kernel.org Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/18535df8-e647-4643-af9a-bb780af03a70@sirena.org.uk Link: https://lore.kernel.org/r/20250720102229.179114-1-maz@kernel.org Signed-off-by: Oliver Upton oliver.upton@linux.dev
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index e54d29feb469..d373d555a69b 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -1169,6 +1169,8 @@ static inline bool __vcpu_read_sys_reg_from_cpu(int reg, u64 *val) * System registers listed in the switch are not saved on every * exit from the guest but are only saved on vcpu_put. * + * SYSREGS_ON_CPU *MUST* be checked before using this helper. + * * Note that MPIDR_EL1 for the guest is set by KVM via VMPIDR_EL2 but * should never be listed below, because the guest cannot modify its * own MPIDR_EL1 and MPIDR_EL1 is accessed for VCPU A from VCPU B's @@ -1221,6 +1223,8 @@ static inline bool __vcpu_write_sys_reg_to_cpu(u64 val, int reg) * System registers listed in the switch are not restored on every * entry to the guest but are only restored on vcpu_load. * + * SYSREGS_ON_CPU *MUST* be checked before using this helper. + * * Note that MPIDR_EL1 for the guest is set by KVM via VMPIDR_EL2 but * should never be listed below, because the MPIDR should only be set * once, before running the VCPU, and never changed later. diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c index 7dafd10e52e8..95d186e0bf54 100644 --- a/arch/arm64/kvm/hyp/exception.c +++ b/arch/arm64/kvm/hyp/exception.c @@ -26,7 +26,8 @@ static inline u64 __vcpu_read_sys_reg(const struct kvm_vcpu *vcpu, int reg)
if (unlikely(vcpu_has_nv(vcpu))) return vcpu_read_sys_reg(vcpu, reg); - else if (__vcpu_read_sys_reg_from_cpu(reg, &val)) + else if (vcpu_get_flag(vcpu, SYSREGS_ON_CPU) && + __vcpu_read_sys_reg_from_cpu(reg, &val)) return val;
return __vcpu_sys_reg(vcpu, reg); @@ -36,7 +37,8 @@ static inline void __vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64 val, int reg) { if (unlikely(vcpu_has_nv(vcpu))) vcpu_write_sys_reg(vcpu, val, reg); - else if (!__vcpu_write_sys_reg_to_cpu(val, reg)) + else if (!vcpu_get_flag(vcpu, SYSREGS_ON_CPU) || + !__vcpu_write_sys_reg_to_cpu(val, reg)) __vcpu_assign_sys_reg(vcpu, reg, val); }