From 0df9dab891ff0d9b646d82e4fe038229e4c02451 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 15 Sep 2023 17:39:15 -0700 Subject: KVM: x86/mmu: Stop zapping invalidated TDP MMU roots asynchronously Stop zapping invalidate TDP MMU roots via work queue now that KVM preserves TDP MMU roots until they are explicitly invalidated. Zapping roots asynchronously was effectively a workaround to avoid stalling a vCPU for an extended during if a vCPU unloaded a root, which at the time happened whenever the guest toggled CR0.WP (a frequent operation for some guest kernels). While a clever hack, zapping roots via an unbound worker had subtle, unintended consequences on host scheduling, especially when zapping multiple roots, e.g. as part of a memslot. Because the work of zapping a root is no longer bound to the task that initiated the zap, things like the CPU affinity and priority of the original task get lost. Losing the affinity and priority can be especially problematic if unbound workqueues aren't affined to a small number of CPUs, as zapping multiple roots can cause KVM to heavily utilize the majority of CPUs in the system, *beyond* the CPUs KVM is already using to run vCPUs. When deleting a memslot via KVM_SET_USER_MEMORY_REGION, the async root zap can result in KVM occupying all logical CPUs for ~8ms, and result in high priority tasks not being scheduled in in a timely manner. In v5.15, which doesn't preserve unloaded roots, the issues were even more noticeable as KVM would zap roots more frequently and could occupy all CPUs for 50ms+. Consuming all CPUs for an extended duration can lead to significant jitter throughout the system, e.g. on ChromeOS with virtio-gpu, deleting memslots is a semi-frequent operation as memslots are deleted and recreated with different host virtual addresses to react to host GPU drivers allocating and freeing GPU blobs. On ChromeOS, the jitter manifests as audio blips during games due to the audio server's tasks not getting scheduled in promptly, despite the tasks having a high realtime priority. Deleting memslots isn't exactly a fast path and should be avoided when possible, and ChromeOS is working towards utilizing MAP_FIXED to avoid the memslot shenanigans, but KVM is squarely in the wrong. Not to mention that removing the async zapping eliminates a non-trivial amount of complexity. Note, one of the subtle behaviors hidden behind the async zapping is that KVM would zap invalidated roots only once (ignoring partial zaps from things like mmu_notifier events). Preserve this behavior by adding a flag to identify roots that are scheduled to be zapped versus roots that have already been zapped but not yet freed. Add a comment calling out why kvm_tdp_mmu_invalidate_all_roots() can encounter invalid roots, as it's not at all obvious why zapping invalidated roots shouldn't simply zap all invalid roots. Reported-by: Pattara Teerapong Cc: David Stevens Cc: Yiwei Zhang Cc: Paul Hsia Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson Message-Id: <20230916003916.2545000-4-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/x86.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) (limited to 'arch/x86/kvm/x86.c') diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 6c9c81e82e65..9f18b06bbda6 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -12308,9 +12308,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) if (ret) goto out; - ret = kvm_mmu_init_vm(kvm); - if (ret) - goto out_page_track; + kvm_mmu_init_vm(kvm); ret = static_call(kvm_x86_vm_init)(kvm); if (ret) @@ -12355,7 +12353,6 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) out_uninit_mmu: kvm_mmu_uninit_vm(kvm); -out_page_track: kvm_page_track_cleanup(kvm); out: return ret; -- cgit v1.2.3-58-ga151 From 73554b29bd70546c1a9efc9c160641ef1b849358 Mon Sep 17 00:00:00 2001 From: Jim Mattson Date: Mon, 25 Sep 2023 17:34:46 +0000 Subject: KVM: x86/pmu: Synthesize at most one PMI per VM-exit When the irq_work callback, kvm_pmi_trigger_fn(), is invoked during a VM-exit that also invokes __kvm_perf_overflow() as a result of instruction emulation, kvm_pmu_deliver_pmi() will be called twice before the next VM-entry. Calling kvm_pmu_deliver_pmi() twice is unlikely to be problematic now that KVM sets the LVTPC mask bit when delivering a PMI. But using IRQ work to trigger the PMI is still broken, albeit very theoretically. E.g. if the self-IPI to trigger IRQ work is be delayed long enough for the vCPU to be migrated to a different pCPU, then it's possible for kvm_pmi_trigger_fn() to race with the kvm_pmu_deliver_pmi() from KVM_REQ_PMI and still generate two PMIs. KVM could set the mask bit using an atomic operation, but that'd just be piling on unnecessary code to workaround what is effectively a hack. The *only* reason KVM uses IRQ work is to ensure the PMI is treated as a wake event, e.g. if the vCPU just executed HLT. Remove the irq_work callback for synthesizing a PMI, and all of the logic for invoking it. Instead, to prevent a vcpu from leaving C0 with a PMI pending, add a check for KVM_REQ_PMI to kvm_vcpu_has_events(). Fixes: 9cd803d496e7 ("KVM: x86: Update vPMCs when retiring instructions") Signed-off-by: Jim Mattson Tested-by: Mingwei Zhang Tested-by: Dapeng Mi Signed-off-by: Mingwei Zhang Link: https://lore.kernel.org/r/20230925173448.3518223-2-mizhang@google.com [sean: massage changelog] Signed-off-by: Sean Christopherson --- arch/x86/include/asm/kvm_host.h | 1 - arch/x86/kvm/pmu.c | 27 +-------------------------- arch/x86/kvm/x86.c | 3 +++ 3 files changed, 4 insertions(+), 27 deletions(-) (limited to 'arch/x86/kvm/x86.c') diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 17715cb8731d..70d139406bc8 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -528,7 +528,6 @@ struct kvm_pmu { u64 raw_event_mask; struct kvm_pmc gp_counters[KVM_INTEL_PMC_MAX_GENERIC]; struct kvm_pmc fixed_counters[KVM_PMC_MAX_FIXED]; - struct irq_work irq_work; /* * Overlay the bitmap with a 64-bit atomic so that all bits can be diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c index edb89b51b383..9ae07db6f0f6 100644 --- a/arch/x86/kvm/pmu.c +++ b/arch/x86/kvm/pmu.c @@ -93,14 +93,6 @@ void kvm_pmu_ops_update(const struct kvm_pmu_ops *pmu_ops) #undef __KVM_X86_PMU_OP } -static void kvm_pmi_trigger_fn(struct irq_work *irq_work) -{ - struct kvm_pmu *pmu = container_of(irq_work, struct kvm_pmu, irq_work); - struct kvm_vcpu *vcpu = pmu_to_vcpu(pmu); - - kvm_pmu_deliver_pmi(vcpu); -} - static inline void __kvm_perf_overflow(struct kvm_pmc *pmc, bool in_pmi) { struct kvm_pmu *pmu = pmc_to_pmu(pmc); @@ -124,20 +116,7 @@ static inline void __kvm_perf_overflow(struct kvm_pmc *pmc, bool in_pmi) __set_bit(pmc->idx, (unsigned long *)&pmu->global_status); } - if (!pmc->intr || skip_pmi) - return; - - /* - * Inject PMI. If vcpu was in a guest mode during NMI PMI - * can be ejected on a guest mode re-entry. Otherwise we can't - * be sure that vcpu wasn't executing hlt instruction at the - * time of vmexit and is not going to re-enter guest mode until - * woken up. So we should wake it, but this is impossible from - * NMI context. Do it from irq work instead. - */ - if (in_pmi && !kvm_handling_nmi_from_guest(pmc->vcpu)) - irq_work_queue(&pmc_to_pmu(pmc)->irq_work); - else + if (pmc->intr && !skip_pmi) kvm_make_request(KVM_REQ_PMI, pmc->vcpu); } @@ -675,9 +654,6 @@ void kvm_pmu_refresh(struct kvm_vcpu *vcpu) void kvm_pmu_reset(struct kvm_vcpu *vcpu) { - struct kvm_pmu *pmu = vcpu_to_pmu(vcpu); - - irq_work_sync(&pmu->irq_work); static_call(kvm_x86_pmu_reset)(vcpu); } @@ -687,7 +663,6 @@ void kvm_pmu_init(struct kvm_vcpu *vcpu) memset(pmu, 0, sizeof(*pmu)); static_call(kvm_x86_pmu_init)(vcpu); - init_irq_work(&pmu->irq_work, kvm_pmi_trigger_fn); pmu->event_count = 0; pmu->need_cleanup = false; kvm_pmu_refresh(vcpu); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 9f18b06bbda6..42a4e8f5e89a 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -12843,6 +12843,9 @@ static inline bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu) return true; #endif + if (kvm_test_request(KVM_REQ_PMI, vcpu)) + return true; + if (kvm_arch_interrupt_allowed(vcpu) && (kvm_cpu_has_interrupt(vcpu) || kvm_guest_apic_has_interrupt(vcpu))) -- cgit v1.2.3-58-ga151 From 18164f66e6c59fda15c198b371fa008431efdb22 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 27 Sep 2023 17:19:52 -0700 Subject: x86/fpu: Allow caller to constrain xfeatures when copying to uabi buffer Plumb an xfeatures mask into __copy_xstate_to_uabi_buf() so that KVM can constrain which xfeatures are saved into the userspace buffer without having to modify the user_xfeatures field in KVM's guest_fpu state. KVM's ABI for KVM_GET_XSAVE{2} is that features that are not exposed to guest must not show up in the effective xstate_bv field of the buffer. Saving only the guest-supported xfeatures allows userspace to load the saved state on a different host with a fewer xfeatures, so long as the target host supports the xfeatures that are exposed to the guest. KVM currently sets user_xfeatures directly to restrict KVM_GET_XSAVE{2} to the set of guest-supported xfeatures, but doing so broke KVM's historical ABI for KVM_SET_XSAVE, which allows userspace to load any xfeatures that are supported by the *host*. Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson Message-Id: <20230928001956.924301-2-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/include/asm/fpu/api.h | 3 ++- arch/x86/kernel/fpu/core.c | 5 +++-- arch/x86/kernel/fpu/xstate.c | 7 +++++-- arch/x86/kernel/fpu/xstate.h | 3 ++- arch/x86/kvm/x86.c | 21 +++++++++------------ 5 files changed, 21 insertions(+), 18 deletions(-) (limited to 'arch/x86/kvm/x86.c') diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h index 31089b851c4f..a2be3aefff9f 100644 --- a/arch/x86/include/asm/fpu/api.h +++ b/arch/x86/include/asm/fpu/api.h @@ -157,7 +157,8 @@ static inline void fpu_update_guest_xfd(struct fpu_guest *guest_fpu, u64 xfd) { static inline void fpu_sync_guest_vmexit_xfd_state(void) { } #endif -extern void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf, unsigned int size, u32 pkru); +extern void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf, + unsigned int size, u64 xfeatures, u32 pkru); extern int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf, u64 xcr0, u32 *vpkru); static inline void fpstate_set_confidential(struct fpu_guest *gfpu) diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index a86d37052a64..a21a4d0ecc34 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -369,14 +369,15 @@ int fpu_swap_kvm_fpstate(struct fpu_guest *guest_fpu, bool enter_guest) EXPORT_SYMBOL_GPL(fpu_swap_kvm_fpstate); void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf, - unsigned int size, u32 pkru) + unsigned int size, u64 xfeatures, u32 pkru) { struct fpstate *kstate = gfpu->fpstate; union fpregs_state *ustate = buf; struct membuf mb = { .p = buf, .left = size }; if (cpu_feature_enabled(X86_FEATURE_XSAVE)) { - __copy_xstate_to_uabi_buf(mb, kstate, pkru, XSTATE_COPY_XSAVE); + __copy_xstate_to_uabi_buf(mb, kstate, xfeatures, pkru, + XSTATE_COPY_XSAVE); } else { memcpy(&ustate->fxsave, &kstate->regs.fxsave, sizeof(ustate->fxsave)); diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index cadf68737e6b..76408313ed7f 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -1049,6 +1049,7 @@ static void copy_feature(bool from_xstate, struct membuf *to, void *xstate, * __copy_xstate_to_uabi_buf - Copy kernel saved xstate to a UABI buffer * @to: membuf descriptor * @fpstate: The fpstate buffer from which to copy + * @xfeatures: The mask of xfeatures to save (XSAVE mode only) * @pkru_val: The PKRU value to store in the PKRU component * @copy_mode: The requested copy mode * @@ -1059,7 +1060,8 @@ static void copy_feature(bool from_xstate, struct membuf *to, void *xstate, * It supports partial copy but @to.pos always starts from zero. */ void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate, - u32 pkru_val, enum xstate_copy_mode copy_mode) + u64 xfeatures, u32 pkru_val, + enum xstate_copy_mode copy_mode) { const unsigned int off_mxcsr = offsetof(struct fxregs_state, mxcsr); struct xregs_state *xinit = &init_fpstate.regs.xsave; @@ -1083,7 +1085,7 @@ void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate, break; case XSTATE_COPY_XSAVE: - header.xfeatures &= fpstate->user_xfeatures; + header.xfeatures &= fpstate->user_xfeatures & xfeatures; break; } @@ -1185,6 +1187,7 @@ void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk, enum xstate_copy_mode copy_mode) { __copy_xstate_to_uabi_buf(to, tsk->thread.fpu.fpstate, + tsk->thread.fpu.fpstate->user_xfeatures, tsk->thread.pkru, copy_mode); } diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h index a4ecb04d8d64..3518fb26d06b 100644 --- a/arch/x86/kernel/fpu/xstate.h +++ b/arch/x86/kernel/fpu/xstate.h @@ -43,7 +43,8 @@ enum xstate_copy_mode { struct membuf; extern void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate, - u32 pkru_val, enum xstate_copy_mode copy_mode); + u64 xfeatures, u32 pkru_val, + enum xstate_copy_mode copy_mode); extern void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk, enum xstate_copy_mode mode); extern int copy_uabi_from_kernel_to_xstate(struct fpstate *fpstate, const void *kbuf, u32 *pkru); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 9f18b06bbda6..41d8e6c8570c 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5382,26 +5382,23 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu, return 0; } -static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu, - struct kvm_xsave *guest_xsave) + +static void kvm_vcpu_ioctl_x86_get_xsave2(struct kvm_vcpu *vcpu, + u8 *state, unsigned int size) { if (fpstate_is_confidential(&vcpu->arch.guest_fpu)) return; - fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu, - guest_xsave->region, - sizeof(guest_xsave->region), + fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu, state, size, + vcpu->arch.guest_fpu.fpstate->user_xfeatures, vcpu->arch.pkru); } -static void kvm_vcpu_ioctl_x86_get_xsave2(struct kvm_vcpu *vcpu, - u8 *state, unsigned int size) +static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu, + struct kvm_xsave *guest_xsave) { - if (fpstate_is_confidential(&vcpu->arch.guest_fpu)) - return; - - fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu, - state, size, vcpu->arch.pkru); + return kvm_vcpu_ioctl_x86_get_xsave2(vcpu, (void *)guest_xsave->region, + sizeof(guest_xsave->region)); } static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu, -- cgit v1.2.3-58-ga151 From 8647c52e9504c99752a39f1d44f6268f82c40a5c Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 27 Sep 2023 17:19:53 -0700 Subject: KVM: x86: Constrain guest-supported xfeatures only at KVM_GET_XSAVE{2} Mask off xfeatures that aren't exposed to the guest only when saving guest state via KVM_GET_XSAVE{2} instead of modifying user_xfeatures directly. Preserving the maximal set of xfeatures in user_xfeatures restores KVM's ABI for KVM_SET_XSAVE, which prior to commit ad856280ddea ("x86/kvm/fpu: Limit guest user_xfeatures to supported bits of XCR0") allowed userspace to load xfeatures that are supported by the host, irrespective of what xfeatures are exposed to the guest. There is no known use case where userspace *intentionally* loads xfeatures that aren't exposed to the guest, but the bug fixed by commit ad856280ddea was specifically that KVM_GET_SAVE{2} would save xfeatures that weren't exposed to the guest, e.g. would lead to userspace unintentionally loading guest-unsupported xfeatures when live migrating a VM. Restricting KVM_SET_XSAVE to guest-supported xfeatures is especially problematic for QEMU-based setups, as QEMU has a bug where instead of terminating the VM if KVM_SET_XSAVE fails, QEMU instead simply stops loading guest state, i.e. resumes the guest after live migration with incomplete guest state, and ultimately results in guest data corruption. Note, letting userspace restore all host-supported xfeatures does not fix setups where a VM is migrated from a host *without* commit ad856280ddea, to a target with a subset of host-supported xfeatures. However there is no way to safely address that scenario, e.g. KVM could silently drop the unsupported features, but that would be a clear violation of KVM's ABI and so would require userspace to opt-in, at which point userspace could simply be updated to sanitize the to-be-loaded XSAVE state. Reported-by: Tyler Stachecki Closes: https://lore.kernel.org/all/20230914010003.358162-1-tstachecki@bloomberg.net Fixes: ad856280ddea ("x86/kvm/fpu: Limit guest user_xfeatures to supported bits of XCR0") Cc: stable@vger.kernel.org Cc: Leonardo Bras Signed-off-by: Sean Christopherson Acked-by: Dave Hansen Message-Id: <20230928001956.924301-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kernel/fpu/xstate.c | 5 +---- arch/x86/kvm/cpuid.c | 8 -------- arch/x86/kvm/x86.c | 18 ++++++++++++++++-- 3 files changed, 17 insertions(+), 14 deletions(-) (limited to 'arch/x86/kvm/x86.c') diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index 76408313ed7f..ef6906107c54 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -1539,10 +1539,7 @@ static int fpstate_realloc(u64 xfeatures, unsigned int ksize, fpregs_restore_userregs(); newfps->xfeatures = curfps->xfeatures | xfeatures; - - if (!guest_fpu) - newfps->user_xfeatures = curfps->user_xfeatures | xfeatures; - + newfps->user_xfeatures = curfps->user_xfeatures | xfeatures; newfps->xfd = curfps->xfd & ~xfeatures; /* Do the final updates within the locked region */ diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 0544e30b4946..773132c3bf5a 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -360,14 +360,6 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu) vcpu->arch.guest_supported_xcr0 = cpuid_get_supported_xcr0(vcpu->arch.cpuid_entries, vcpu->arch.cpuid_nent); - /* - * FP+SSE can always be saved/restored via KVM_{G,S}ET_XSAVE, even if - * XSAVE/XCRO are not exposed to the guest, and even if XSAVE isn't - * supported by the host. - */ - vcpu->arch.guest_fpu.fpstate->user_xfeatures = vcpu->arch.guest_supported_xcr0 | - XFEATURE_MASK_FPSSE; - kvm_update_pv_runtime(vcpu); vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 41d8e6c8570c..1e645f5b1e2c 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5386,12 +5386,26 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu, static void kvm_vcpu_ioctl_x86_get_xsave2(struct kvm_vcpu *vcpu, u8 *state, unsigned int size) { + /* + * Only copy state for features that are enabled for the guest. The + * state itself isn't problematic, but setting bits in the header for + * features that are supported in *this* host but not exposed to the + * guest can result in KVM_SET_XSAVE failing when live migrating to a + * compatible host without the features that are NOT exposed to the + * guest. + * + * FP+SSE can always be saved/restored via KVM_{G,S}ET_XSAVE, even if + * XSAVE/XCRO are not exposed to the guest, and even if XSAVE isn't + * supported by the host. + */ + u64 supported_xcr0 = vcpu->arch.guest_supported_xcr0 | + XFEATURE_MASK_FPSSE; + if (fpstate_is_confidential(&vcpu->arch.guest_fpu)) return; fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu, state, size, - vcpu->arch.guest_fpu.fpstate->user_xfeatures, - vcpu->arch.pkru); + supported_xcr0, vcpu->arch.pkru); } static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu, -- cgit v1.2.3-58-ga151