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[104.155.91.135]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4922fa891acsm3867895e9.9.2026.06.15.09.25.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Jun 2026 09:25:23 -0700 (PDT) Date: Mon, 15 Jun 2026 17:25:20 +0100 From: Vincent Donnefort To: tabba@google.com Cc: Marc Zyngier , Oliver Upton , Will Deacon , Catalin Marinas , Quentin Perret , Sebastian Ene , Per Larsen , Suzuki K Poulose , Zenghui Yu , Joey Gouly , Steffen Eiden , Mark Rutland , Jonathan Cameron , Hyunwoo Kim , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1 11/11] KVM: arm64: Implement lazy vCPU state sync for non-protected guests Message-ID: References: <20260612065925.755562-1-tabba@google.com> <20260612065925.755562-12-tabba@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260612065925.755562-12-tabba@google.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260615_092527_440199_C2DBA0F4 X-CRM114-Status: GOOD ( 41.08 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Jun 12, 2026 at 07:59:25AM +0100, tabba@google.com wrote: > pKVM copies a non-protected guest's register context between the host > and the hypervisor on every world switch, even when the host never > inspects it. Defer the copy: on entry, flush the host context into the > hyp vCPU only when the host marked it dirty (PKVM_HOST_STATE_DIRTY); on > exit, leave it in the hyp vCPU and copy it back only when the host needs > it, via a __pkvm_vcpu_sync_state hypercall on trap handling or at vcpu > put. A protected guest's context is copied as before, since lazy sync > only helps where the host is trusted to see the guest's registers. > > The PC is the exception: it is copied back on every exit so the > kvm_exit tracepoint reports the guest's real exit PC rather than the > value left by the previous sync. > > Signed-off-by: Fuad Tabba > --- > arch/arm64/include/asm/kvm_asm.h | 1 + > arch/arm64/include/asm/kvm_host.h | 2 + > arch/arm64/kvm/arm.c | 7 +++ > arch/arm64/kvm/handle_exit.c | 22 ++++++++ > arch/arm64/kvm/hyp/nvhe/hyp-main.c | 88 ++++++++++++++++++++++++++++-- > 5 files changed, 115 insertions(+), 5 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h > index 043495f7fc78..6e1135b3ded4 100644 > --- a/arch/arm64/include/asm/kvm_asm.h > +++ b/arch/arm64/include/asm/kvm_asm.h > @@ -113,6 +113,7 @@ enum __kvm_host_smccc_func { > __KVM_HOST_SMCCC_FUNC___pkvm_finalize_teardown_vm, > __KVM_HOST_SMCCC_FUNC___pkvm_vcpu_load, > __KVM_HOST_SMCCC_FUNC___pkvm_vcpu_put, > + __KVM_HOST_SMCCC_FUNC___pkvm_vcpu_sync_state, > __KVM_HOST_SMCCC_FUNC___pkvm_tlb_flush_vmid, > > MARKER(__KVM_HOST_SMCCC_FUNC_MAX) > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index a49042bfa801..1ef660774adc 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -1113,6 +1113,8 @@ struct kvm_vcpu_arch { > /* SError pending for nested guest */ > #define NESTED_SERROR_PENDING __vcpu_single_flag(sflags, BIT(8)) > > +/* pKVM host vcpu state is dirty, needs resync (nVHE-only) */ nit: with hVHE, I guess we can just drop that nVHE-only? > +#define PKVM_HOST_STATE_DIRTY __vcpu_single_flag(iflags, BIT(4)) > > /* Pointer to the vcpu's SVE FFR for sve_{save,load}_state() */ > #define vcpu_sve_pffr(vcpu) (kern_hyp_va((vcpu)->arch.sve_state) + \ > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > index c9f36932c980..a5c54e37778b 100644 > --- a/arch/arm64/kvm/arm.c > +++ b/arch/arm64/kvm/arm.c > @@ -734,6 +734,10 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) > if (is_protected_kvm_enabled()) { > kvm_call_hyp(__vgic_v3_save_aprs, &vcpu->arch.vgic_cpu.vgic_v3); > kvm_call_hyp_nvhe(__pkvm_vcpu_put); > + > + /* __pkvm_vcpu_put implies a sync of the state */ > + if (!kvm_vm_is_protected(vcpu->kvm)) > + vcpu_set_flag(vcpu, PKVM_HOST_STATE_DIRTY); > } > > kvm_vcpu_put_debug(vcpu); > @@ -961,6 +965,9 @@ int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu) > return ret; > > if (is_protected_kvm_enabled()) { > + /* Start with the vcpu in a dirty state */ > + if (!kvm_vm_is_protected(vcpu->kvm)) > + vcpu_set_flag(vcpu, PKVM_HOST_STATE_DIRTY); > ret = pkvm_create_hyp_vm(kvm); > if (ret) > return ret; > diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c > index 54aedf93c78b..dccc3786548b 100644 > --- a/arch/arm64/kvm/handle_exit.c > +++ b/arch/arm64/kvm/handle_exit.c > @@ -422,6 +422,21 @@ static int handle_trap_exceptions(struct kvm_vcpu *vcpu) > { > int handled; > > + /* > + * If we run a non-protected VM when protection is enabled > + * system-wide, resync the state from the hypervisor and mark > + * it as dirty on the host side if it wasn't dirty already > + * (which could happen if preemption has taken place). > + */ > + if (is_protected_kvm_enabled() && !kvm_vm_is_protected(vcpu->kvm)) { > + preempt_disable(); nit: since we are introducing guard() with that series, this one could be guard(preempt)(). > + if (!(vcpu_get_flag(vcpu, PKVM_HOST_STATE_DIRTY))) { > + kvm_call_hyp_nvhe(__pkvm_vcpu_sync_state); > + vcpu_set_flag(vcpu, PKVM_HOST_STATE_DIRTY); > + } > + preempt_enable(); > + } > + > /* > * See ARM ARM B1.14.1: "Hyp traps on instructions > * that fail their condition code check" > @@ -489,6 +504,13 @@ int handle_exit(struct kvm_vcpu *vcpu, int exception_index) > /* For exit types that need handling before we can be preempted */ > void handle_exit_early(struct kvm_vcpu *vcpu, int exception_index) > { > + /* > + * We just exited, so the state is clean from a hypervisor > + * perspective. > + */ > + if (is_protected_kvm_enabled()) > + vcpu_clear_flag(vcpu, PKVM_HOST_STATE_DIRTY); > + > if (ARM_SERROR_PENDING(exception_index)) { > if (this_cpu_has_cap(ARM64_HAS_RAS_EXTN)) { > u64 disr = kvm_vcpu_get_disr(vcpu); > diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > index 23e644c24a03..02383b372258 100644 > --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c > +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > @@ -139,6 +139,49 @@ static void sync_hyp_vgic_state(struct pkvm_hyp_vcpu *hyp_vcpu) > host_cpu_if->vgic_lr[i] = hyp_cpu_if->vgic_lr[i]; > } > > + > +static void __copy_vcpu_state(const struct kvm_vcpu *from_vcpu, > + struct kvm_vcpu *to_vcpu) > +{ > + int i; > + > + to_vcpu->arch.ctxt.regs = from_vcpu->arch.ctxt.regs; > + to_vcpu->arch.ctxt.spsr_abt = from_vcpu->arch.ctxt.spsr_abt; > + to_vcpu->arch.ctxt.spsr_und = from_vcpu->arch.ctxt.spsr_und; > + to_vcpu->arch.ctxt.spsr_irq = from_vcpu->arch.ctxt.spsr_irq; > + to_vcpu->arch.ctxt.spsr_fiq = from_vcpu->arch.ctxt.spsr_fiq; > + to_vcpu->arch.ctxt.fp_regs = from_vcpu->arch.ctxt.fp_regs; > + > + /* > + * Copy the sysregs, but don't mess with the timer state which > + * is directly handled by EL1 and is expected to be preserved. > + * enum vcpu_sysreg is sparse: VNCR-mapped registers take values > + * derived from their VNCR page offset, so the timer registers do > + * not form a contiguous numeric range and must be skipped by name. > + */ > + for (i = 1; i < NR_SYS_REGS; i++) { > + switch (i) { > + case CNTVOFF_EL2: > + case CNTV_CVAL_EL0: > + case CNTV_CTL_EL0: > + case CNTP_CVAL_EL0: > + case CNTP_CTL_EL0: > + continue; > + } > + to_vcpu->arch.ctxt.sys_regs[i] = from_vcpu->arch.ctxt.sys_regs[i]; > + } > +} > + > +static void __sync_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu) > +{ > + __copy_vcpu_state(&hyp_vcpu->vcpu, hyp_vcpu->host_vcpu); > +} > + > +static void __flush_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu) > +{ > + __copy_vcpu_state(hyp_vcpu->host_vcpu, &hyp_vcpu->vcpu); > +} nit: Could that be flush/sync_hyp_vcpu_state? as everything this is called "state" and we already have flush_debug_state() below ? > + > static void flush_debug_state(struct pkvm_hyp_vcpu *hyp_vcpu) > { > struct kvm_vcpu *host_vcpu = hyp_vcpu->host_vcpu; > @@ -168,7 +211,17 @@ static void flush_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu) > fpsimd_sve_flush(); > flush_debug_state(hyp_vcpu); > > - hyp_vcpu->vcpu.arch.ctxt = host_vcpu->arch.ctxt; > + /* > + * If we deal with a non-protected guest and the state is potentially > + * dirty (from a host perspective), copy the state back into the hyp > + * vcpu. > + */ > + if (!pkvm_hyp_vcpu_is_protected(hyp_vcpu)) { > + if (vcpu_get_flag(host_vcpu, PKVM_HOST_STATE_DIRTY)) > + __flush_hyp_vcpu(hyp_vcpu); > + } else { > + hyp_vcpu->vcpu.arch.ctxt = host_vcpu->arch.ctxt; > + } > > hyp_vcpu->vcpu.arch.mdcr_el2 = host_vcpu->arch.mdcr_el2; > hyp_vcpu->vcpu.arch.hcr_el2 &= ~(HCR_TWI | HCR_TWE); > @@ -191,9 +244,11 @@ static void sync_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu) > fpsimd_sve_sync(&hyp_vcpu->vcpu); > sync_debug_state(hyp_vcpu); > > - host_vcpu->arch.ctxt = hyp_vcpu->vcpu.arch.ctxt; > - > - host_vcpu->arch.hcr_el2 = hyp_vcpu->vcpu.arch.hcr_el2; > + if (pkvm_hyp_vcpu_is_protected(hyp_vcpu)) > + host_vcpu->arch.ctxt = hyp_vcpu->vcpu.arch.ctxt; > + else > + /* Keep the PC current for the kvm_exit tracepoint (lazy ctxt sync). */ > + host_vcpu->arch.ctxt.regs.pc = hyp_vcpu->vcpu.arch.ctxt.regs.pc; > > host_vcpu->arch.fault = hyp_vcpu->vcpu.arch.fault; > > @@ -227,8 +282,30 @@ static void handle___pkvm_vcpu_put(struct kvm_cpu_context *host_ctxt) > { > struct pkvm_hyp_vcpu *hyp_vcpu = pkvm_get_loaded_hyp_vcpu(); > > - if (hyp_vcpu) > + if (hyp_vcpu) { > + struct kvm_vcpu *host_vcpu = hyp_vcpu->host_vcpu; > + > + if (!pkvm_hyp_vcpu_is_protected(hyp_vcpu) && > + !vcpu_get_flag(host_vcpu, PKVM_HOST_STATE_DIRTY)) { > + __sync_hyp_vcpu(hyp_vcpu); > + } > + > pkvm_put_hyp_vcpu(hyp_vcpu); > + } > +} > + > +static void handle___pkvm_vcpu_sync_state(struct kvm_cpu_context *host_ctxt) > +{ > + struct pkvm_hyp_vcpu *hyp_vcpu; > + > + if (!is_protected_kvm_enabled()) > + return; Since "KVM: arm64: Remove is_protected_kvm_enabled() checks from hypercalls" we got rid of those is_protected_kvm_enabled() for pKVM-only HVCs. (also, it is declared in the pKVM-only section of the HVCs) > + > + hyp_vcpu = pkvm_get_loaded_hyp_vcpu(); > + if (!hyp_vcpu || pkvm_hyp_vcpu_is_protected(hyp_vcpu)) > + return; > + > + __sync_hyp_vcpu(hyp_vcpu); > } > > static struct kvm_vcpu *__get_host_hyp_vcpus(struct kvm_vcpu *arg, > @@ -859,6 +936,7 @@ static const hcall_t host_hcall[] = { > HANDLE_FUNC(__pkvm_finalize_teardown_vm), > HANDLE_FUNC(__pkvm_vcpu_load), > HANDLE_FUNC(__pkvm_vcpu_put), > + HANDLE_FUNC(__pkvm_vcpu_sync_state), > HANDLE_FUNC(__pkvm_tlb_flush_vmid), > }; > > -- > 2.54.0.1136.gdb2ca164c4-goog >