From nobody Sun Feb 8 12:36:48 2026 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 24BEA2E11D7 for ; Thu, 16 Oct 2025 20:04:28 +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=1760645069; cv=none; b=E/tSVo2y729ttNsqaK+DJUFkCod0sb8GaiVVH6al0ECFHG88A7OC2KoaOqKMZs0DNcsvtr2z9qs3IIbCaANnt+DKGDLnxbEuy8cRJjcbDGs2qQCQ9yTvFSZ3E4x83CQ9dMkjcmYUdRg/qqP0NFY8WwGRw6Jj6/Lc3SiNjmD7OHs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760645069; c=relaxed/simple; bh=SNE+nRiwqlE038YuWxnWn7j7iJTACVTLDjxXYnTjtWg=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=tGtiKK7gJ4ftQNUlZ6Ou+TazzuNTmXpzsSz4kmNqGSel0XrtJ95FVt+pmUHNofyR0phA8GrqL0QgOawXRaIM5OAqN9Guo0P94OfYhufIQLveEc8I+t+18DrCq8QTRtz3iGxq5rtaxhiylxnms1/11e0B1QPAbUrAINFOKFchxrg= 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=zrqw8pOF; 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="zrqw8pOF" Received: by mail-pj1-f73.google.com with SMTP id 98e67ed59e1d1-336b9f3b5b0so1287930a91.3 for ; Thu, 16 Oct 2025 13:04:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1760645067; x=1761249867; 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=8iJumIyoa7Jv1Ta1I07laKkWSuZSFDfZ4MoevL3qjrU=; b=zrqw8pOFo3pEeVjTnQoxMEYdTfWiLOpZ/1K7fAo9llED2PdDSbZE9wBESp9U2tPDOE Ial4OmVODB3+alwPHRgD9rEV8JQsjzw9N1Vym6O5QTFlCZfYhB1zoAp2LNSGxglxRriU aq3pXs8IvYTPpf9oFyKfyYt+B+ziDbs+aU5FJX8bgG/KMHJo21ZonyiGt8g66wagIGpG qBxqQKvvzxWZLHJnxatZme6ZIiZKdqz14ACWMB/xxQnpoWTkq7mSlbXQFOQtIvl8cpk7 VgVeO8XXSWglQ+yFN+tX2Zdu00FDxpyhKmsESei3AQlxCy9nxNwDG4sjsNwf7xGbVzIZ rKIQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1760645067; x=1761249867; 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=8iJumIyoa7Jv1Ta1I07laKkWSuZSFDfZ4MoevL3qjrU=; b=TMK7t7/HH8jIAa93Z60ctDx5TOnc1UivLCIkmQhLOcBGi2FRVEAZzHyW/pSGuFePnE bFznu/9lOEKo7jtoI4iHHjt7JRQtrhf1sS1TBjDg5jRZNBeu6PAZ7GDUXotgBGOOTeLx Ozfy3wCMQMCsKvZH1rkOlzP2eKrBvdHPo02cnUqOzo/unZ6isjLvzisoq4I38/ctLaPR 2Jiy1wgyKXuiaj7v2R2gf87M+6noQXoaTUq80MJny8GfrZO/GZ0IUm35iDiKaI7jSbfP cAh014pqWmTNOcYIf9E8Lce9RBkfx0pNVSeUi0A0RkSPdDgUu47MZUCToVGzx8nlsRD4 bvgA== X-Forwarded-Encrypted: i=1; AJvYcCXYMt+dwm/asz3oWtWO17YCZVAGZgCprc4vf5NOvgbOlcKNj8JB0jFgP5EUh1rfo0iRh7iOXAgtLQL5+zo=@vger.kernel.org X-Gm-Message-State: AOJu0YxyAEUWWdD0EIofoDbWIxFOC7uiURO/Qy6StMetHo2BRHfZobD2 LIM5z6szu1Hh3MOs/hg7ZAwPEUMl/Lktc0opJgoTuPouWAnYKeUaYRM0+aXja0H8evnQ9gyggGB Y8cxdjg== X-Google-Smtp-Source: AGHT+IGOG6A5Ijw3KLuRGlwFU7ZiWO+4sv+3A/3GnT2Oqt8U2ps3rXOjLFbWGQRyn9sJEkzA80a7CZbegDY= X-Received: from pjkm1.prod.google.com ([2002:a17:90a:7301:b0:339:ee20:f620]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:3fcc:b0:31e:d4e3:4002 with SMTP id 98e67ed59e1d1-33bcf85ad9amr1009215a91.2.1760645067487; Thu, 16 Oct 2025 13:04:27 -0700 (PDT) Reply-To: Sean Christopherson Date: Thu, 16 Oct 2025 13:04:17 -0700 In-Reply-To: <20251016200417.97003-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20251016200417.97003-1-seanjc@google.com> X-Mailer: git-send-email 2.51.0.858.gf9c4a03a3a-goog Message-ID: <20251016200417.97003-5-seanjc@google.com> Subject: [PATCH v3 4/4] KVM: x86: Unify L1TF flushing under per-CPU variable From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Pawan Gupta , Brendan Jackman Content-Transfer-Encoding: quoted-printable 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_hos= t.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=3D0) */ bool preempted_in_kernel; =20 - /* 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; =20 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)); =20 - vcpu->arch.l1tf_flush_l1d =3D true; + kvm_request_l1tf_flush_l1d(); if (!flags) { trace_kvm_page_fault(vcpu, fault_address, error_code); =20 diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 3fca63a261f5..468a013d9ef3 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -3880,7 +3880,7 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool= launch) goto vmentry_failed; =20 /* Hide L1D cache contents from the nested guest. */ - vcpu->arch.l1tf_flush_l1d =3D true; + kvm_request_l1tf_flush_l1d(); =20 /* * 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 e91d99211efe..0347d321a86e 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -395,26 +395,16 @@ static noinstr bool vmx_l1d_flush(struct kvm_vcpu *vc= pu) * '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 =3D vcpu->arch.l1tf_flush_l1d; - vcpu->arch.l1tf_flush_l1d =3D false; - - /* - * Clear the per-cpu flush bit, it gets set again from - * the interrupt handlers. - */ - flush_l1d |=3D kvm_get_cpu_l1tf_flush_l1d(); + if (!kvm_get_cpu_l1tf_flush_l1d()) + return; kvm_clear_cpu_l1tf_flush_l1d(); - - if (!flush_l1d) - return false; } =20 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 cp= u) { struct kvm_pmu *pmu =3D vcpu_to_pmu(vcpu); =20 - vcpu->arch.l1tf_flush_l1d =3D true; + kvm_request_l1tf_flush_l1d(); =20 if (vcpu->scheduled_out && pmu->version && pmu->event_count) { pmu->need_cleanup =3D 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 =3D true; + kvm_request_l1tf_flush_l1d(); =20 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, gp= a_t cr2_or_gpa, return handle_emulation_failure(vcpu, emulation_type); } =20 - vcpu->arch.l1tf_flush_l1d =3D true; + kvm_request_l1tf_flush_l1d(); =20 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); } =20 +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); =20 u64 get_kvmclock_ns(struct kvm *kvm); --=20 2.51.0.858.gf9c4a03a3a-goog