The KVM_CHECK_EXTENSION ioctl can be issued either on the global fd (/dev/kvm), or on the VM fd obtained with KVM_CREATE_VM. For most extensions, KVM returns the same value with either method, but for some of them it can refine the returned value depending on the VM type. The KVM documentation [1] advises to use the VM fd:
Based on their initialization different VMs may have different capabilities. It is thus encouraged to use the vm ioctl to query for capabilities (available with KVM_CAP_CHECK_EXTENSION_VM on the vm fd) Ongoing work on Arm confidential VMs confirms this, as some capabilities become unavailable to confidential VMs, requiring changes in QEMU to use kvm_vm_check_extension() instead of kvm_check_extension() [2]. Rather than changing each check one by one, change kvm_check_extension() to always issue the ioctl on the VM fd when available, and remove kvm_vm_check_extension(). Fall back to the global fd when the VM check is unavailable: * Ancient kernels do not support KVM_CHECK_EXTENSION on the VM fd, since it was added by commit 92b591a4c46b ("KVM: Allow KVM_CHECK_EXTENSION on the vm fd") in Linux 3.17 [3]. Support for Linux 3.16 ended in June 2020, but there may still be old images around. * A couple of calls must be issued before the VM fd is available, since they determine the VM type: KVM_CAP_MIPS_VZ and KVM_CAP_ARM_VM_IPA_SIZE Does any user actually depend on the check being done on the global fd instead of the VM fd? I surveyed all cases where KVM presently returns different values depending on the query method. Luckily QEMU already calls kvm_vm_check_extension() for most of those. Only three of them are ambiguous, because currently done on the global fd: * KVM_CAP_MAX_VCPUS and KVM_CAP_MAX_VCPU_ID on Arm, changes value if the user requests a vGIC different from the default. But QEMU queries this before vGIC configuration, so the reported value will be the same. * KVM_CAP_SW_TLB on PPC. When issued on the global fd, returns false if the kvm-hv module is loaded; when issued on the VM fd, returns false only if the VM type is HV instead of PR. If this returns false, then QEMU will fail to initialize a BOOKE206 MMU model. So this patch supposedly improves things, as it allows to run this type of vCPU even when both KVM modules are loaded. * KVM_CAP_PPC_SECURE_GUEST. Similarly, doing this check on a VM fd refines the returned value, and ensures that SVM is actually supported. Since QEMU follows the check with kvm_vm_enable_cap(), this patch should only provide better error reporting. [1] https://www.kernel.org/doc/html/latest/virt/kvm/api.html#kvm-check-extension [2] https://lore.kernel.org/kvm/875ybi0ytc....@redhat.com/ [3] https://github.com/torvalds/linux/commit/92b591a4c46b Cc: Marcelo Tosatti <mtosa...@redhat.com> Cc: Nicholas Piggin <npig...@gmail.com> Cc: Daniel Henrique Barboza <danielhb...@gmail.com> Cc: qemu-...@nongnu.org Suggested-by: Cornelia Huck <coh...@redhat.com> Signed-off-by: Jean-Philippe Brucker <jean-phili...@linaro.org> --- v1: https://lore.kernel.org/qemu-devel/20230421163822.839167-1-jean-phili...@linaro.org/ v1->v2: Initialize check_extension_vm using kvm_vm_ioctl() as suggested --- include/sysemu/kvm.h | 2 -- include/sysemu/kvm_int.h | 1 + accel/kvm/kvm-all.c | 34 +++++++++++++++------------------- target/arm/kvm.c | 2 +- target/i386/kvm/kvm.c | 6 +++--- target/ppc/kvm.c | 36 ++++++++++++++++++------------------ 6 files changed, 38 insertions(+), 43 deletions(-) diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h index c6f34d4794..df97077434 100644 --- a/include/sysemu/kvm.h +++ b/include/sysemu/kvm.h @@ -404,8 +404,6 @@ bool kvm_arch_stop_on_emulation_error(CPUState *cpu); int kvm_check_extension(KVMState *s, unsigned int extension); -int kvm_vm_check_extension(KVMState *s, unsigned int extension); - #define kvm_vm_enable_cap(s, capability, cap_flags, ...) \ ({ \ struct kvm_enable_cap cap = { \ diff --git a/include/sysemu/kvm_int.h b/include/sysemu/kvm_int.h index cad763e240..fa4c9aeb96 100644 --- a/include/sysemu/kvm_int.h +++ b/include/sysemu/kvm_int.h @@ -123,6 +123,7 @@ struct KVMState uint16_t xen_gnttab_max_frames; uint16_t xen_evtchn_max_pirq; char *device; + bool check_extension_vm; }; void kvm_memory_listener_register(KVMState *s, KVMMemoryListener *kml, diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c index e08dd04164..3d9fbc8a98 100644 --- a/accel/kvm/kvm-all.c +++ b/accel/kvm/kvm-all.c @@ -1128,7 +1128,11 @@ int kvm_check_extension(KVMState *s, unsigned int extension) { int ret; - ret = kvm_ioctl(s, KVM_CHECK_EXTENSION, extension); + if (!s->check_extension_vm) { + ret = kvm_ioctl(s, KVM_CHECK_EXTENSION, extension); + } else { + ret = kvm_vm_ioctl(s, KVM_CHECK_EXTENSION, extension); + } if (ret < 0) { ret = 0; } @@ -1136,19 +1140,6 @@ int kvm_check_extension(KVMState *s, unsigned int extension) return ret; } -int kvm_vm_check_extension(KVMState *s, unsigned int extension) -{ - int ret; - - ret = kvm_vm_ioctl(s, KVM_CHECK_EXTENSION, extension); - if (ret < 0) { - /* VM wide version not implemented, use global one instead */ - ret = kvm_check_extension(s, extension); - } - - return ret; -} - /* * We track the poisoned pages to be able to: * - replace them on VM reset @@ -1515,10 +1506,10 @@ static int kvm_dirty_ring_init(KVMState *s) * Read the max supported pages. Fall back to dirty logging mode * if the dirty ring isn't supported. */ - ret = kvm_vm_check_extension(s, capability); + ret = kvm_check_extension(s, capability); if (ret <= 0) { capability = KVM_CAP_DIRTY_LOG_RING_ACQ_REL; - ret = kvm_vm_check_extension(s, capability); + ret = kvm_check_extension(s, capability); } if (ret <= 0) { @@ -1541,7 +1532,7 @@ static int kvm_dirty_ring_init(KVMState *s) } /* Enable the backup bitmap if it is supported */ - ret = kvm_vm_check_extension(s, KVM_CAP_DIRTY_LOG_RING_WITH_BITMAP); + ret = kvm_check_extension(s, KVM_CAP_DIRTY_LOG_RING_WITH_BITMAP); if (ret > 0) { ret = kvm_vm_enable_cap(s, KVM_CAP_DIRTY_LOG_RING_WITH_BITMAP, 0); if (ret) { @@ -2360,7 +2351,7 @@ static void kvm_irqchip_create(KVMState *s) */ static int kvm_recommended_vcpus(KVMState *s) { - int ret = kvm_vm_check_extension(s, KVM_CAP_NR_VCPUS); + int ret = kvm_check_extension(s, KVM_CAP_NR_VCPUS); return (ret) ? ret : 4; } @@ -2526,6 +2517,11 @@ static int kvm_init(MachineState *ms) s->vmfd = ret; + ret = kvm_vm_ioctl(s, KVM_CHECK_EXTENSION, KVM_CAP_CHECK_EXTENSION_VM); + if (ret > 0) { + s->check_extension_vm = true; + } + /* check the vcpu limits */ soft_vcpus_limit = kvm_recommended_vcpus(s); hard_vcpus_limit = kvm_max_vcpus(s); @@ -2668,7 +2664,7 @@ static int kvm_init(MachineState *ms) memory_listener_register(&kvm_io_listener, &address_space_io); - s->sync_mmu = !!kvm_vm_check_extension(kvm_state, KVM_CAP_SYNC_MMU); + s->sync_mmu = !!kvm_check_extension(kvm_state, KVM_CAP_SYNC_MMU); if (!s->sync_mmu) { ret = ram_block_discard_disable(true); assert(!ret); diff --git a/target/arm/kvm.c b/target/arm/kvm.c index ab85d628a8..3371ffa401 100644 --- a/target/arm/kvm.c +++ b/target/arm/kvm.c @@ -582,7 +582,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s) if (s->kvm_eager_split_size) { uint32_t sizes; - sizes = kvm_vm_check_extension(s, KVM_CAP_ARM_SUPPORTED_BLOCK_SIZES); + sizes = kvm_check_extension(s, KVM_CAP_ARM_SUPPORTED_BLOCK_SIZES); if (!sizes) { s->kvm_eager_split_size = 0; warn_report("Eager Page Split support not available"); diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index e68cbe9293..f16229d0a8 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -163,7 +163,7 @@ static int kvm_get_one_msr(X86CPU *cpu, int index, uint64_t *value); bool kvm_has_smm(void) { - return kvm_vm_check_extension(kvm_state, KVM_CAP_X86_SMM); + return kvm_check_extension(kvm_state, KVM_CAP_X86_SMM); } bool kvm_has_adjust_clock_stable(void) @@ -2697,7 +2697,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s) return ret; } } - if (kvm_vm_check_extension(s, KVM_CAP_X86_USER_SPACE_MSR)) { + if (kvm_check_extension(s, KVM_CAP_X86_USER_SPACE_MSR)) { bool r; ret = kvm_vm_enable_cap(s, KVM_CAP_X86_USER_SPACE_MSR, 0, @@ -5236,7 +5236,7 @@ static bool __kvm_enable_sgx_provisioning(KVMState *s) { int fd, ret; - if (!kvm_vm_check_extension(s, KVM_CAP_SGX_ATTRIBUTE)) { + if (!kvm_check_extension(s, KVM_CAP_SGX_ATTRIBUTE)) { return false; } diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c index 8231feb2d4..0699030a6f 100644 --- a/target/ppc/kvm.c +++ b/target/ppc/kvm.c @@ -101,7 +101,7 @@ static uint32_t debug_inst_opcode; static bool kvmppc_is_pr(KVMState *ks) { /* Assume KVM-PR if the GET_PVINFO capability is available */ - return kvm_vm_check_extension(ks, KVM_CAP_PPC_GET_PVINFO) != 0; + return kvm_check_extension(ks, KVM_CAP_PPC_GET_PVINFO) != 0; } static int kvm_ppc_register_host_cpu_type(void); @@ -118,11 +118,11 @@ int kvm_arch_init(MachineState *ms, KVMState *s) cap_interrupt_unset = kvm_check_extension(s, KVM_CAP_PPC_UNSET_IRQ); cap_segstate = kvm_check_extension(s, KVM_CAP_PPC_SEGSTATE); cap_booke_sregs = kvm_check_extension(s, KVM_CAP_PPC_BOOKE_SREGS); - cap_ppc_smt_possible = kvm_vm_check_extension(s, KVM_CAP_PPC_SMT_POSSIBLE); + cap_ppc_smt_possible = kvm_check_extension(s, KVM_CAP_PPC_SMT_POSSIBLE); cap_spapr_tce = kvm_check_extension(s, KVM_CAP_SPAPR_TCE); cap_spapr_tce_64 = kvm_check_extension(s, KVM_CAP_SPAPR_TCE_64); cap_spapr_multitce = kvm_check_extension(s, KVM_CAP_SPAPR_MULTITCE); - cap_spapr_vfio = kvm_vm_check_extension(s, KVM_CAP_SPAPR_TCE_VFIO); + cap_spapr_vfio = kvm_check_extension(s, KVM_CAP_SPAPR_TCE_VFIO); cap_one_reg = kvm_check_extension(s, KVM_CAP_ONE_REG); cap_hior = kvm_check_extension(s, KVM_CAP_PPC_HIOR); cap_epr = kvm_check_extension(s, KVM_CAP_PPC_EPR); @@ -131,23 +131,23 @@ int kvm_arch_init(MachineState *ms, KVMState *s) * Note: we don't set cap_papr here, because this capability is * only activated after this by kvmppc_set_papr() */ - cap_htab_fd = kvm_vm_check_extension(s, KVM_CAP_PPC_HTAB_FD); + cap_htab_fd = kvm_check_extension(s, KVM_CAP_PPC_HTAB_FD); cap_fixup_hcalls = kvm_check_extension(s, KVM_CAP_PPC_FIXUP_HCALL); - cap_ppc_smt = kvm_vm_check_extension(s, KVM_CAP_PPC_SMT); - cap_htm = kvm_vm_check_extension(s, KVM_CAP_PPC_HTM); - cap_mmu_radix = kvm_vm_check_extension(s, KVM_CAP_PPC_MMU_RADIX); - cap_mmu_hash_v3 = kvm_vm_check_extension(s, KVM_CAP_PPC_MMU_HASH_V3); - cap_xive = kvm_vm_check_extension(s, KVM_CAP_PPC_IRQ_XIVE); - cap_resize_hpt = kvm_vm_check_extension(s, KVM_CAP_SPAPR_RESIZE_HPT); + cap_ppc_smt = kvm_check_extension(s, KVM_CAP_PPC_SMT); + cap_htm = kvm_check_extension(s, KVM_CAP_PPC_HTM); + cap_mmu_radix = kvm_check_extension(s, KVM_CAP_PPC_MMU_RADIX); + cap_mmu_hash_v3 = kvm_check_extension(s, KVM_CAP_PPC_MMU_HASH_V3); + cap_xive = kvm_check_extension(s, KVM_CAP_PPC_IRQ_XIVE); + cap_resize_hpt = kvm_check_extension(s, KVM_CAP_SPAPR_RESIZE_HPT); kvmppc_get_cpu_characteristics(s); - cap_ppc_nested_kvm_hv = kvm_vm_check_extension(s, KVM_CAP_PPC_NESTED_HV); + cap_ppc_nested_kvm_hv = kvm_check_extension(s, KVM_CAP_PPC_NESTED_HV); cap_large_decr = kvmppc_get_dec_bits(); - cap_fwnmi = kvm_vm_check_extension(s, KVM_CAP_PPC_FWNMI); + cap_fwnmi = kvm_check_extension(s, KVM_CAP_PPC_FWNMI); /* * Note: setting it to false because there is not such capability * in KVM at this moment. * - * TODO: call kvm_vm_check_extension() with the right capability + * TODO: call kvm_check_extension() with the right capability * after the kernel starts implementing it. */ cap_ppc_pvr_compat = false; @@ -157,8 +157,8 @@ int kvm_arch_init(MachineState *ms, KVMState *s) exit(1); } - cap_rpt_invalidate = kvm_vm_check_extension(s, KVM_CAP_PPC_RPT_INVALIDATE); - cap_ail_mode_3 = kvm_vm_check_extension(s, KVM_CAP_PPC_AIL_MODE_3); + cap_rpt_invalidate = kvm_check_extension(s, KVM_CAP_PPC_RPT_INVALIDATE); + cap_ail_mode_3 = kvm_check_extension(s, KVM_CAP_PPC_AIL_MODE_3); kvm_ppc_register_host_cpu_type(); return 0; @@ -1969,7 +1969,7 @@ static int kvmppc_get_pvinfo(CPUPPCState *env, struct kvm_ppc_pvinfo *pvinfo) { CPUState *cs = env_cpu(env); - if (kvm_vm_check_extension(cs->kvm_state, KVM_CAP_PPC_GET_PVINFO) && + if (kvm_check_extension(cs->kvm_state, KVM_CAP_PPC_GET_PVINFO) && !kvm_vm_ioctl(cs->kvm_state, KVM_PPC_GET_PVINFO, pvinfo)) { return 0; } @@ -2289,7 +2289,7 @@ int kvmppc_reset_htab(int shift_hint) /* Full emulation, tell caller to allocate htab itself */ return 0; } - if (kvm_vm_check_extension(kvm_state, KVM_CAP_PPC_ALLOC_HTAB)) { + if (kvm_check_extension(kvm_state, KVM_CAP_PPC_ALLOC_HTAB)) { int ret; ret = kvm_vm_ioctl(kvm_state, KVM_PPC_ALLOCATE_HTAB, &shift); if (ret == -ENOTTY) { @@ -2474,7 +2474,7 @@ static void kvmppc_get_cpu_characteristics(KVMState *s) cap_ppc_safe_bounds_check = 0; cap_ppc_safe_indirect_branch = 0; - ret = kvm_vm_check_extension(s, KVM_CAP_PPC_GET_CPU_CHAR); + ret = kvm_check_extension(s, KVM_CAP_PPC_GET_CPU_CHAR); if (!ret) { return; } -- 2.44.0