From 0f559cd91e37b7978e4198ca2fbf7eb95df11361 Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Mon, 10 Nov 2025 17:30:10 +0000 Subject: [PATCH 1/2] KVM: arm64: Finalize ID registers only once per VM Owing to the ID registers being global to the VM, there is no point in computing them more than once. However, recent changes making use of kvm_set_vm_id_reg() outlined that we repeatedly hammer the ID registers when we shouldn't. Gate the ID reg update on the VM having never run. Fixes: 50e7cce81b9b2 ("KVM: arm64: Limit clearing of ID_{AA64PFR0,PFR1}_EL1.GIC to userspace irqchip") Fixes: 5cb57a1aff755 ("KVM: arm64: Zero ID_AA64PFR0_EL1.GIC when no GICv3 is presented to the guest") Closes: https://lore.kernel.org/r/aRHf6x5umkTYhYJ3@finisterre.sirena.org.uk Reported-by: Mark Brown Tested-by: Mark Brown Link: https://patch.msgid.link/20251110173010.1918424-1-maz@kernel.org Signed-off-by: Marc Zyngier --- arch/arm64/kvm/sys_regs.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c index 8ae2bca81614..ec3fbe0b8d52 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -5609,7 +5609,11 @@ int kvm_finalize_sys_regs(struct kvm_vcpu *vcpu) guard(mutex)(&kvm->arch.config_lock); - if (!irqchip_in_kernel(kvm)) { + /* + * This hacks into the ID registers, so only perform it when the + * first vcpu runs, or the kvm_set_vm_id_reg() helper will scream. + */ + if (!irqchip_in_kernel(kvm) && !kvm_vm_has_ran_once(kvm)) { u64 val; val = kvm_read_vm_id_reg(kvm, SYS_ID_AA64PFR0_EL1) & ~ID_AA64PFR0_EL1_GIC; From 85592114ffda568b507bc2b04f5e9afbe7c13b62 Mon Sep 17 00:00:00 2001 From: Alexandru Elisei Date: Wed, 12 Nov 2025 10:28:53 +0000 Subject: [PATCH 2/2] KVM: arm64: VHE: Compute fgt traps before activating them On VHE, the Fine Grain Traps registers are written to hardware in kvm_arch_vcpu_load()->..->__activate_traps_hfgxtr(), but the fgt array is computed later, in kvm_vcpu_load_fgt(). This can lead to zero being written to the FGT registers the first time a VCPU is loaded. Also, any changes to the fgt array will be visible only after the VCPU is scheduled out, and then back in, which is not the intended behaviour. Fix it by computing the fgt array just before the fgt traps are written to hardware. Fixes: fb10ddf35c1c ("KVM: arm64: Compute per-vCPU FGTs at vcpu_load()") Signed-off-by: Alexandru Elisei Reviewed-by: Oliver Upton Link: https://patch.msgid.link/20251112102853.47759-1-alexandru.elisei@arm.com Signed-off-by: Marc Zyngier --- arch/arm64/kvm/arm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index 870953b4a8a7..052bf0d4d0b0 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -624,6 +624,7 @@ nommu: kvm_timer_vcpu_load(vcpu); kvm_vgic_load(vcpu); kvm_vcpu_load_debug(vcpu); + kvm_vcpu_load_fgt(vcpu); if (has_vhe()) kvm_vcpu_load_vhe(vcpu); kvm_arch_vcpu_load_fp(vcpu); @@ -642,7 +643,6 @@ nommu: vcpu->arch.hcr_el2 |= HCR_TWI; vcpu_set_pauth_traps(vcpu); - kvm_vcpu_load_fgt(vcpu); if (is_protected_kvm_enabled()) { kvm_call_hyp_nvhe(__pkvm_vcpu_load,