From 39d61b46adfd784f601534a6d488697bf53f2633 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 31 Jan 2025 17:38:25 -0800 Subject: [PATCH] KVM: x86: Remove per-vCPU "cache" of its reference pvclock Remove the per-vCPU "cache" of the reference pvclock and instead cache only the TSC shift+multiplier. All other fields in pvclock are fully recomputed by kvm_guest_time_update(), i.e. aren't actually persisted. In addition to shaving a few bytes, explicitly tracking the TSC shift/mul fields makes it easier to see that those fields are tied to hw_tsc_khz (they exist to avoid having to do expensive math in the common case). And conversely, not tracking the other fields makes it easier to see that things like the version number are pulled from the guest's copy, not from KVM's reference. Reviewed-by: Paul Durrant Link: https://lore.kernel.org/r/20250201013827.680235-10-seanjc@google.com Signed-off-by: Sean Christopherson --- arch/x86/include/asm/kvm_host.h | 3 ++- arch/x86/kvm/x86.c | 27 +++++++++++++++------------ arch/x86/kvm/xen.c | 8 ++++---- 3 files changed, 21 insertions(+), 17 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index b15cde0a9b5c..14b2d033925e 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -908,7 +908,8 @@ struct kvm_vcpu_arch { int (*complete_userspace_io)(struct kvm_vcpu *vcpu); gpa_t time; - struct pvclock_vcpu_time_info hv_clock; + s8 pvclock_tsc_shift; + u32 pvclock_tsc_mul; unsigned int hw_tsc_khz; struct gfn_to_pfn_cache pv_time; /* set guest stopped flag in pvclock flags field */ diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 597abd5429af..bdc6f449f192 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3170,6 +3170,7 @@ static void kvm_setup_guest_pvclock(struct pvclock_vcpu_time_info *ref_hv_clock, static int kvm_guest_time_update(struct kvm_vcpu *v) { + struct pvclock_vcpu_time_info hv_clock = {}; unsigned long flags, tgt_tsc_khz; unsigned seq; struct kvm_vcpu_arch *vcpu = &v->arch; @@ -3247,20 +3248,22 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) if (unlikely(vcpu->hw_tsc_khz != tgt_tsc_khz)) { kvm_get_time_scale(NSEC_PER_SEC, tgt_tsc_khz * 1000LL, - &vcpu->hv_clock.tsc_shift, - &vcpu->hv_clock.tsc_to_system_mul); + &vcpu->pvclock_tsc_shift, + &vcpu->pvclock_tsc_mul); vcpu->hw_tsc_khz = tgt_tsc_khz; kvm_xen_update_tsc_info(v); } - vcpu->hv_clock.tsc_timestamp = tsc_timestamp; - vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset; + hv_clock.tsc_shift = vcpu->pvclock_tsc_shift; + hv_clock.tsc_to_system_mul = vcpu->pvclock_tsc_mul; + hv_clock.tsc_timestamp = tsc_timestamp; + hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset; vcpu->last_guest_tsc = tsc_timestamp; /* If the host uses TSC clocksource, then it is stable */ - vcpu->hv_clock.flags = 0; + hv_clock.flags = 0; if (use_master_clock) - vcpu->hv_clock.flags |= PVCLOCK_TSC_STABLE_BIT; + hv_clock.flags |= PVCLOCK_TSC_STABLE_BIT; if (vcpu->pv_time.active) { /* @@ -3269,24 +3272,24 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) * is active/enabled. */ if (vcpu->pvclock_set_guest_stopped_request) { - vcpu->hv_clock.flags |= PVCLOCK_GUEST_STOPPED; + hv_clock.flags |= PVCLOCK_GUEST_STOPPED; vcpu->pvclock_set_guest_stopped_request = false; } - kvm_setup_guest_pvclock(&vcpu->hv_clock, v, &vcpu->pv_time, 0, false); + kvm_setup_guest_pvclock(&hv_clock, v, &vcpu->pv_time, 0, false); - vcpu->hv_clock.flags &= ~PVCLOCK_GUEST_STOPPED; + hv_clock.flags &= ~PVCLOCK_GUEST_STOPPED; } #ifdef CONFIG_KVM_XEN if (vcpu->xen.vcpu_info_cache.active) - kvm_setup_guest_pvclock(&vcpu->hv_clock, v, &vcpu->xen.vcpu_info_cache, + kvm_setup_guest_pvclock(&hv_clock, v, &vcpu->xen.vcpu_info_cache, offsetof(struct compat_vcpu_info, time), xen_pvclock_tsc_unstable); if (vcpu->xen.vcpu_time_info_cache.active) - kvm_setup_guest_pvclock(&vcpu->hv_clock, v, &vcpu->xen.vcpu_time_info_cache, 0, + kvm_setup_guest_pvclock(&hv_clock, v, &vcpu->xen.vcpu_time_info_cache, 0, xen_pvclock_tsc_unstable); #endif - kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock); + kvm_hv_setup_tsc_page(v->kvm, &hv_clock); return 0; } diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c index 300a79f1fae5..2801c7bcc2ef 100644 --- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -176,8 +176,8 @@ static int xen_get_guest_pvclock(struct kvm_vcpu *vcpu, * Sanity check TSC shift+multiplier to verify the guest's view of time * is more or less consistent. */ - if (hv_clock->tsc_shift != vcpu->arch.hv_clock.tsc_shift || - hv_clock->tsc_to_system_mul != vcpu->arch.hv_clock.tsc_to_system_mul) + if (hv_clock->tsc_shift != vcpu->arch.pvclock_tsc_shift || + hv_clock->tsc_to_system_mul != vcpu->arch.pvclock_tsc_mul) return -EINVAL; return 0; @@ -2316,8 +2316,8 @@ void kvm_xen_update_tsc_info(struct kvm_vcpu *vcpu) entry = kvm_find_cpuid_entry_index(vcpu, function, 1); if (entry) { - entry->ecx = vcpu->arch.hv_clock.tsc_to_system_mul; - entry->edx = vcpu->arch.hv_clock.tsc_shift; + entry->ecx = vcpu->arch.pvclock_tsc_mul; + entry->edx = vcpu->arch.pvclock_tsc_shift; } entry = kvm_find_cpuid_entry_index(vcpu, function, 2); -- 2.50.1