From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f73.google.com (mail-pj1-f73.google.com [209.85.216.73]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E1BF323184A for ; Fri, 31 Oct 2025 00:31:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.73 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761870662; cv=none; b=QBYx57N5+GiOu32MMT0u3LhRzdk9/BU06C7QSQemWGzuoJ9hD/mK1Vaf57r70JyqAZnIRcP7aDst7Pe8Crf7kbCL4s5NVBVKu/TPNIg0dJF1ypZzoWnJP28ijHZBv7dJB2bxm5E57Iumb1gAVxo4N35Yp9M8C+0hAsMCFSopE/k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761870662; c=relaxed/simple; bh=RT/sHTj0KzhQejEjxZna5Y25pQzofKvau2oAC0XFLaw=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=YApKlL5QsjWMLsZhMSxWHwA2xG/vhhPzRE8Fy1LjcWzDAn/jC6VRRw0KydeJW/FaLG15PVyf16R7lwi4MGSz4iZw55SqghE2aH8Bb7dhRN3PMeSmV6B1mEnuRbEwkzgWKG7F/rbM31pI2Hv8wREHS5O5FwKxqOjSKqy7bID3xLY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=TZpi9qhF; arc=none smtp.client-ip=209.85.216.73 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="TZpi9qhF" Received: by mail-pj1-f73.google.com with SMTP id 98e67ed59e1d1-33bc5d7c289so3040577a91.0 for ; Thu, 30 Oct 2025 17:31:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1761870660; x=1762475460; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:from:to:cc:subject:date:message-id:reply-to; bh=LbTsWO94j2FTsRt3NBHviHWz1y0m9u2EeuxD0YgFUA4=; b=TZpi9qhFK+2O1C3GQijopQgJMlMLtGga7+AqwSHkJvMxQPN724rnyE+PlzRQ+NsVBf adB0KdVoHD8ANTKbvCMcKcBmFNApJPZFt7VDoWS49c3CBGzS3rqRf12tAV53FDafb+85 E6XL1/gKN31qy4p9gcPqR49nWCiwoXFXpziH0Zq+uIK8dUmtbz9RSi3z5LE7xpG01CWl LbgpG2v420R/EWNpw+VCT73hfxKYG+XI+tkskoPH5/tzSXwesSECLsR/HfTsN0AEzmMk +AviEr025TIbazYPS4ZJmVpV3QwbwVK8DiOHGp0awOZy093QHWlSBCQILceFKbjo95hq jtKg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1761870660; x=1762475460; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=LbTsWO94j2FTsRt3NBHviHWz1y0m9u2EeuxD0YgFUA4=; b=cCpKhvoFBX/j164stXw7OagP/3UpXrhhi5ZKGR17Eas1c5JwhizMTnopJYT3A/GWAm o4EvgNuhHn8D1wia2ZBr+UAlJkzhBBwL+5QBuTwYYFY4iv9yi6q2Ai+67rRBz/aee/hI SNYn1c8slOlg5FGX3OGFqv9fV0EMPtAFE0mPZyUEA1yG7I2PZIP+1KAzOqGBtBDVUPQc D1rkMbzdPq65uGJsOBvvfR/UpP1pbhoL2CxrqmPq3Oxch3Px6nE0L9ihhOhxTU3vzYtT WOk7TCB9SAup2xzBNXlxDmFSn2PucA5BdLmn4wF9Fm2v85DB9+8OVxFhAvnFgSwrkWvE 1RUg== X-Gm-Message-State: AOJu0YwX82gI4hPo8DVXLCc4JG0ZzttiMIgX+ywzoJGtucJOzKW3weDc 3liqq3mrFPPTg0fe5CqvanmNqWBVZfiEo7frGhnF3urUapEcG8F4E2PQv64z42apipHoel5YFUK wgEAn7A== X-Google-Smtp-Source: AGHT+IG9niXeqcQKc5xfb5DpFxjBvH7jNOuHlLCtg8NMqPQ9wNkIMDEwIxItwd+jCVHQRiKCwCLg7bs2U5Y= X-Received: from plblq15.prod.google.com ([2002:a17:903:144f:b0:268:11e:8271]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:ea0e:b0:292:39b4:e785 with SMTP id d9443c01a7336-2951a3e696fmr21856645ad.26.1761870660376; Thu, 30 Oct 2025 17:31:00 -0700 (PDT) Reply-To: Sean Christopherson Date: Thu, 30 Oct 2025 17:30:40 -0700 In-Reply-To: <20251031003040.3491385-1-seanjc@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20251031003040.3491385-1-seanjc@google.com> X-Mailer: git-send-email 2.51.1.930.gacf6e81ea2-goog Message-ID: <20251031003040.3491385-9-seanjc@google.com> Subject: [PATCH v4 8/8] KVM: x86: Unify L1TF flushing under per-CPU variable From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini , Thomas Gleixner , Borislav Petkov , Peter Zijlstra , Josh Poimboeuf Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Pawan Gupta , Brendan Jackman Content-Type: text/plain; charset="UTF-8" From: Brendan Jackman Currently the tracking of the need to flush L1D for L1TF is tracked by two bits: one per-CPU and one per-vCPU. The per-vCPU bit is always set when the vCPU shows up on a core, so there is no interesting state that's truly per-vCPU. Indeed, this is a requirement, since L1D is a part of the physical CPU. So simplify this by combining the two bits. The vCPU bit was being written from preemption-enabled regions. To play nice with those cases, wrap all calls from KVM and use a raw write so that request a flush with preemption enabled doesn't trigger what would effectively be DEBUG_PREEMPT false positives. Preemption doesn't need to be disabled, as kvm_arch_vcpu_load() will mark the new CPU as needing a flush if the vCPU task is migrated, or if userspace runs the vCPU on a different task. Signed-off-by: Brendan Jackman [sean: put raw write in KVM instead of in a hardirq.h variant] Signed-off-by: Sean Christopherson --- arch/x86/include/asm/kvm_host.h | 3 --- arch/x86/kvm/mmu/mmu.c | 2 +- arch/x86/kvm/vmx/nested.c | 2 +- arch/x86/kvm/vmx/vmx.c | 20 +++++--------------- arch/x86/kvm/x86.c | 6 +++--- arch/x86/kvm/x86.h | 14 ++++++++++++++ 6 files changed, 24 insertions(+), 23 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 48598d017d6f..fcdc65ab13d8 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1055,9 +1055,6 @@ struct kvm_vcpu_arch { /* be preempted when it's in kernel-mode(cpl=0) */ bool preempted_in_kernel; - /* Flush the L1 Data cache for L1TF mitigation on VMENTER */ - bool l1tf_flush_l1d; - /* Host CPU on which VM-entry was most recently attempted */ int last_vmentry_cpu; diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 18d69d48bc55..4e016582adc7 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4859,7 +4859,7 @@ int kvm_handle_page_fault(struct kvm_vcpu *vcpu, u64 error_code, */ BUILD_BUG_ON(lower_32_bits(PFERR_SYNTHETIC_MASK)); - vcpu->arch.l1tf_flush_l1d = true; + kvm_request_l1tf_flush_l1d(); if (!flags) { trace_kvm_page_fault(vcpu, fault_address, error_code); diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index b0cd745518b4..6f2f969d19f9 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -3828,7 +3828,7 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch) goto vmentry_failed; /* Hide L1D cache contents from the nested guest. */ - vcpu->arch.l1tf_flush_l1d = true; + kvm_request_l1tf_flush_l1d(); /* * Must happen outside of nested_vmx_enter_non_root_mode() as it will diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 1b5540105e4b..f87af1836ea1 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -395,26 +395,16 @@ static noinstr void vmx_l1d_flush(struct kvm_vcpu *vcpu) * 'always' */ if (static_branch_likely(&vmx_l1d_flush_cond)) { - bool flush_l1d; - /* - * Clear the per-vcpu flush bit, it gets set again if the vCPU + * Clear the per-cpu flush bit, it gets set again if the vCPU * is reloaded, i.e. if the vCPU is scheduled out or if KVM * exits to userspace, or if KVM reaches one of the unsafe - * VMEXIT handlers, e.g. if KVM calls into the emulator. + * VMEXIT handlers, e.g. if KVM calls into the emulator, + * or from the interrupt handlers. */ - flush_l1d = vcpu->arch.l1tf_flush_l1d; - vcpu->arch.l1tf_flush_l1d = false; - - /* - * Clear the per-cpu flush bit, it gets set again from - * the interrupt handlers. - */ - flush_l1d |= kvm_get_cpu_l1tf_flush_l1d(); + if (!kvm_get_cpu_l1tf_flush_l1d()) + return; kvm_clear_cpu_l1tf_flush_l1d(); - - if (!flush_l1d) - return; } vcpu->stat.l1d_flush++; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index b4b5d2d09634..851f078cd5ca 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5189,7 +5189,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) { struct kvm_pmu *pmu = vcpu_to_pmu(vcpu); - vcpu->arch.l1tf_flush_l1d = true; + kvm_request_l1tf_flush_l1d(); if (vcpu->scheduled_out && pmu->version && pmu->event_count) { pmu->need_cleanup = true; @@ -7999,7 +7999,7 @@ int kvm_write_guest_virt_system(struct kvm_vcpu *vcpu, gva_t addr, void *val, unsigned int bytes, struct x86_exception *exception) { /* kvm_write_guest_virt_system can pull in tons of pages. */ - vcpu->arch.l1tf_flush_l1d = true; + kvm_request_l1tf_flush_l1d(); return kvm_write_guest_virt_helper(addr, val, bytes, vcpu, PFERR_WRITE_MASK, exception); @@ -9395,7 +9395,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, return handle_emulation_failure(vcpu, emulation_type); } - vcpu->arch.l1tf_flush_l1d = true; + kvm_request_l1tf_flush_l1d(); if (!(emulation_type & EMULTYPE_NO_DECODE)) { kvm_clear_exception_queue(vcpu); diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h index f3dc77f006f9..cd67ccbb747f 100644 --- a/arch/x86/kvm/x86.h +++ b/arch/x86/kvm/x86.h @@ -420,6 +420,20 @@ static inline bool kvm_check_has_quirk(struct kvm *kvm, u64 quirk) return !(kvm->arch.disabled_quirks & quirk); } +static __always_inline void kvm_request_l1tf_flush_l1d(void) +{ +#if IS_ENABLED(CONFIG_CPU_MITIGATIONS) && IS_ENABLED(CONFIG_KVM_INTEL) + /* + * Use a raw write to set the per-CPU flag, as KVM will ensure a flush + * even if preemption is currently enabled.. If the current vCPU task + * is migrated to a different CPU (or userspace runs the vCPU on a + * different task) before the next VM-Entry, then kvm_arch_vcpu_load() + * will request a flush on the new CPU. + */ + raw_cpu_write(irq_stat.kvm_cpu_l1tf_flush_l1d, 1); +#endif +} + void kvm_inject_realmode_interrupt(struct kvm_vcpu *vcpu, int irq, int inc_eip); u64 get_kvmclock_ns(struct kvm *kvm); -- 2.51.1.930.gacf6e81ea2-goog