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V" , Emi Kisanuki , Vishal Annapurve , WeiLin.Chang@arm.com, Lorenzo.Pieralisi2@arm.com Subject: [PATCH v14 24/44] KVM: arm64: Handle realm MMIO emulation Date: Wed, 13 May 2026 14:17:32 +0100 Message-ID: <20260513131757.116630-25-steven.price@arm.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260513131757.116630-1-steven.price@arm.com> References: <20260513131757.116630-1-steven.price@arm.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit MMIO emulation for a realm cannot be done directly with the VM's registers as they are protected from the host. However, for emulatable data aborts, the RMM uses GPRS[0] to provide the read/written value. We can transfer this from/to the equivalent VCPU's register entry and then depend on the generic MMIO handling code in KVM. For a MMIO read, the value is placed in the shared RecExit structure during kvm_handle_mmio_return() rather than in the VCPU's register entry. Signed-off-by: Steven Price Reviewed-by: Gavin Shan Reviewed-by: Suzuki K Poulose --- Changes since v7: * New comment for rec_exit_sync_dabt() explaining the call to vcpu_set_reg(). Changes since v5: * Inject SEA to the guest is an emulatable MMIO access triggers a data abort. * kvm_handle_mmio_return() - disable kvm_incr_pc() for a REC (as the PC isn't under the host's control) and move the REC_ENTER_EMULATED_MMIO flag setting to this location (as that tells the RMM to skip the instruction). --- arch/arm64/kvm/inject_fault.c | 4 +++- arch/arm64/kvm/mmio.c | 16 ++++++++++++---- arch/arm64/kvm/rmi-exit.c | 14 ++++++++++++++ 3 files changed, 29 insertions(+), 5 deletions(-) diff --git a/arch/arm64/kvm/inject_fault.c b/arch/arm64/kvm/inject_fault.c index 89982bd3345f..6492397b73d7 100644 --- a/arch/arm64/kvm/inject_fault.c +++ b/arch/arm64/kvm/inject_fault.c @@ -228,7 +228,9 @@ static void inject_abt32(struct kvm_vcpu *vcpu, bool is_pabt, u32 addr) static void __kvm_inject_sea(struct kvm_vcpu *vcpu, bool iabt, u64 addr) { - if (vcpu_el1_is_32bit(vcpu)) + if (unlikely(vcpu_is_rec(vcpu))) + vcpu->arch.rec.run->enter.flags |= REC_ENTER_FLAG_INJECT_SEA; + else if (vcpu_el1_is_32bit(vcpu)) inject_abt32(vcpu, iabt, addr); else inject_abt64(vcpu, iabt, addr); diff --git a/arch/arm64/kvm/mmio.c b/arch/arm64/kvm/mmio.c index e2285ed8c91d..6a8cb927fcca 100644 --- a/arch/arm64/kvm/mmio.c +++ b/arch/arm64/kvm/mmio.c @@ -6,6 +6,7 @@ #include #include +#include #include #include "trace.h" @@ -138,14 +139,21 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu) trace_kvm_mmio(KVM_TRACE_MMIO_READ, len, run->mmio.phys_addr, &data); data = vcpu_data_host_to_guest(vcpu, data, len); - vcpu_set_reg(vcpu, kvm_vcpu_dabt_get_rd(vcpu), data); + + if (vcpu_is_rec(vcpu)) + vcpu->arch.rec.run->enter.gprs[0] = data; + else + vcpu_set_reg(vcpu, kvm_vcpu_dabt_get_rd(vcpu), data); } /* * The MMIO instruction is emulated and should not be re-executed * in the guest. */ - kvm_incr_pc(vcpu); + if (vcpu_is_rec(vcpu)) + vcpu->arch.rec.run->enter.flags |= REC_ENTER_FLAG_EMULATED_MMIO; + else + kvm_incr_pc(vcpu); return 1; } @@ -167,14 +175,14 @@ int io_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa) * No valid syndrome? Ask userspace for help if it has * volunteered to do so, and bail out otherwise. * - * In the protected VM case, there isn't much userspace can do + * In the protected/realm VM case, there isn't much userspace can do * though, so directly deliver an exception to the guest. */ if (!kvm_vcpu_dabt_isvalid(vcpu)) { trace_kvm_mmio_nisv(*vcpu_pc(vcpu), esr, kvm_vcpu_get_hfar(vcpu), fault_ipa); - if (vcpu_is_protected(vcpu)) + if (vcpu_is_protected(vcpu) || vcpu_is_rec(vcpu)) return kvm_inject_sea_dabt(vcpu, kvm_vcpu_get_hfar(vcpu)); if (test_bit(KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER, diff --git a/arch/arm64/kvm/rmi-exit.c b/arch/arm64/kvm/rmi-exit.c index e7c51b6cf6ce..8ec0d179eba2 100644 --- a/arch/arm64/kvm/rmi-exit.c +++ b/arch/arm64/kvm/rmi-exit.c @@ -25,6 +25,20 @@ static int rec_exit_reason_notimpl(struct kvm_vcpu *vcpu) static int rec_exit_sync_dabt(struct kvm_vcpu *vcpu) { + struct realm_rec *rec = &vcpu->arch.rec; + + /* + * In the case of a write, copy over gprs[0] to the target GPR, + * preparing to handle MMIO write fault. The content to be written has + * been saved to gprs[0] by the RMM (even if another register was used + * by the guest). In the case of normal memory access this is redundant + * (the guest will replay the instruction), but the overhead is + * minimal. + */ + if (kvm_vcpu_dabt_iswrite(vcpu) && kvm_vcpu_dabt_isvalid(vcpu)) + vcpu_set_reg(vcpu, kvm_vcpu_dabt_get_rd(vcpu), + rec->run->exit.gprs[0]); + return kvm_handle_guest_abort(vcpu); } -- 2.43.0