From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D04FD29CE9 for ; Fri, 11 Sep 2026 10:59:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789124348; cv=none; b=a4ZDqKq7E8jpUX5cuFHB4OrfA9Bnom1fSnLQnTIbOtgFIWmtKYBs3bmc5Gd7+6Zt1pjiHLv8GN62FB5pbAP9fiP4CuB6+7S8RZTFXjdlX2Rr8YD43ho/Zg98c/v+DSfxhJ5QJ1vCQcK6BIGBEkq6JRM6xhuJMeCSpz9NsgSyCRw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789124348; c=relaxed/simple; bh=goyXvENrkl9cL/kkDSm3v5/IsmDwKwKw90XA0wc82fQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jAn9eCB5RxLIenxGOBwSKxa3SAHSH3/zEN/A+LUR3u0TDyjBgG0EErbzcvlcl5WqsR8D2bJ5Uc68AfLl2qwzLAfrkfgx0gLoki8apY0yiOEFWtrzLfHoRm7CDif6Ke5393u4CB+aPfve5jD//+FNExxdUBZ79KVgpPDDCjervbs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UBR3NPET; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="UBR3NPET" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A9CCF1F00899; Fri, 11 Sep 2026 10:59:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789124346; bh=YbnZ+yPnhdxWX11j6HJb42+gyYAF/mAAozVVD2L6GiI=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=UBR3NPETwUPJR5Ra/VRAoe6XkXD203vXimJNb8fq0x0t4czhDZ5i6BGA/D6xttTWO ahu4A0YkNcrtfFcClnF/lAGRHRyP8+YIwrzKU5UMogYzlfjGo/DhVMkOHpVF09t5Gr u6R1IUKJAhir9ehFES8fXHRXpug+F2bhKqJw4sKpc1krbklbLRtRUsn75rH2hwbDkA owBRQ+DcjyueutlYE/3Gnvj+Q3FSMOyhwIshbeMwNDrXktloUH+MgBA/dwKSISRt/g S6Ee08/lutRT5i8aWhoplRpiVluYH+6YdTwSh0KLa4FrB7d6ABi2gdOO3irxFKwAYp Q82Pb27R0SGxw== From: Sasha Levin To: stable@vger.kernel.org Cc: Marc Zyngier , sashiko-bot@kernel.org, Yuan Yao , Oliver Upton , Sasha Levin Subject: [PATCH 6.18.y 2/2] KVM: arm64: Handle VNCR TLB invalidation race with vcpu_put() VNCR unmapping Date: Fri, 11 Sep 2026 06:59:03 -0400 Message-ID: <20260911105903.296829-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260911105903.296829-1-sashal@kernel.org> References: <2026090924-dweeb-huskiness-bd94@gregkh> <20260911105903.296829-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Marc Zyngier [ Upstream commit 38640bc32be3fcf9526d477155bc19d3f146231f ] While VNCR TLB invalidation always occurs under the MMU lock, vcpu_put() doesn't, while it unmaps the VNCR page. The problem is that the invalidation evaluates vncr_tlb::cpu to decide whether an unmapping needs to take place (cpu != -1) before performing it. On the other hand, this_cpu_reset_vncr_fixmap() unconditionally unmaps if L1_VNCR_MAPPED is set. These two obviously can race, with a TOCTOU pattern on the TLBI path, and a BUG_ON() on the vcpu_put() path. And the two can end-up calling vncr_fixmap(-1), with extra lethal effects. Move the reset of vncr_tlb::cpu to -1 to a common function, and make this update atomic so that only a single thread can reset the field and perform the corresponding unmap. The vcpu_put() still need to unconditionally unmap the current VNCR to close another ugly race. Finally, the assignment of vncr_tlb::cpu is moved to be kept in sync with the actual mapping, similar to L1_VNCR_MAPPED being set. Fixes: 7270cc9157f47 ("KVM: arm64: nv: Handle VNCR_EL2 invalidation from MMU notifiers") Reported-by: sashiko-bot@kernel.org Link: https://lore.kernel.org/r/20260801130237.0FD8F1F00ACA@smtp.kernel.org Signed-off-by: Marc Zyngier Cc: stable@vger.kernel.org Reviewed-by: Yuan Yao Link: https://patch.msgid.link/20260806091026.620700-6-maz@kernel.org Signed-off-by: Oliver Upton Signed-off-by: Sasha Levin --- arch/arm64/kvm/nested.c | 42 +++++++++++++++++++++++++++++++---------- 1 file changed, 32 insertions(+), 10 deletions(-) diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c index 5a297c16bc338..747aad09a40ee 100644 --- a/arch/arm64/kvm/nested.c +++ b/arch/arm64/kvm/nested.c @@ -27,7 +27,7 @@ struct vncr_tlb { bool hpa_writable; /* -1 when not mapped on a CPU */ - int cpu; + atomic_t cpu; /* * true if the TLB is valid. Can only be changed with the @@ -771,16 +771,40 @@ void kvm_vcpu_load_hw_mmu(struct kvm_vcpu *vcpu) } } +/* + * Unmapping an L1 VNCR can happen concurrently without the mmu lock being + * effective (vcpu_put() vs TLBI handling). The atomic_xchg below ensures + * that only one CPU sets it to -1 while getting a valid CPU number back. + */ +static int unmap_l1_vncr(struct vncr_tlb *vt) +{ + int cpu = atomic_xchg_relaxed(&vt->cpu, -1); + + if (cpu != -1) + clear_fixmap(vncr_fixmap(cpu)); + + return cpu; +} + static void this_cpu_reset_vncr_fixmap(struct kvm_vcpu *vcpu) { if (!host_data_test_flag(L1_VNCR_MAPPED)) return; - BUG_ON(vcpu->arch.vncr_tlb->cpu != smp_processor_id()); BUG_ON(is_hyp_ctxt(vcpu)); - clear_fixmap(vncr_fixmap(vcpu->arch.vncr_tlb->cpu)); - vcpu->arch.vncr_tlb->cpu = -1; + /* + * Unconditionally unmap the local VNCR if we have lost the race + * against a concurrent TLBI. Otherwise we could end-up running + * another vcpu with VNCR still mapped if the TLBI thread is + * preempted between the exchange and the clear_fixmap(). + * + * Note that we do not care about the TLBI nuking the fixmap behind + * the back of an running vcpu. This will only generate a fault and + * possibly a retranslation. + */ + if (unmap_l1_vncr(vcpu->arch.vncr_tlb) == -1) + clear_fixmap(vncr_fixmap(smp_processor_id())); host_data_clear_flag(L1_VNCR_MAPPED); atomic_dec(&vcpu->kvm->arch.vncr_map_count); } @@ -870,8 +894,7 @@ u16 get_asid_by_regime(struct kvm_vcpu *vcpu, enum trans_regime regime) static void invalidate_vncr(struct vncr_tlb *vt) { vt->valid = false; - if (vt->cpu != -1) - clear_fixmap(vncr_fixmap(vt->cpu)); + unmap_l1_vncr(vt); } static bool vncr_tlb_intersects(struct vncr_tlb *vt, u64 addr, @@ -1321,7 +1344,7 @@ static int kvm_translate_vncr(struct kvm_vcpu *vcpu, bool *is_gmem) vt->hpa = pfn << PAGE_SHIFT; vt->hpa_writable = writable; vt->valid = true; - vt->cpu = -1; + atomic_set(&vt->cpu, -1); kvm_make_request(KVM_REQ_MAP_L1_VNCR_EL2, vcpu); kvm_release_faultin_page(vcpu->kvm, page, false, vt->wr.pw && vt->hpa_writable); @@ -1452,8 +1475,6 @@ static void kvm_map_l1_vncr(struct kvm_vcpu *vcpu) if (vt->wr.nG && get_asid_by_regime(vcpu, TR_EL20) != vt->wr.asid) return; - vt->cpu = smp_processor_id(); - if (vt->hpa_writable && vt->wr.pw && vt->wr.pr) prot = PAGE_KERNEL; else if (vt->wr.pr) @@ -1468,7 +1489,8 @@ static void kvm_map_l1_vncr(struct kvm_vcpu *vcpu) * FIXME: WO doesn't work at all, need POE support in the kernel. */ if (pgprot_val(prot) != pgprot_val(PAGE_NONE)) { - __set_fixmap(vncr_fixmap(vt->cpu), vt->hpa, prot); + atomic_set(&vt->cpu, smp_processor_id()); + __set_fixmap(vncr_fixmap(atomic_read(&vt->cpu)), vt->hpa, prot); host_data_set_flag(L1_VNCR_MAPPED); atomic_inc(&vcpu->kvm->arch.vncr_map_count); } -- 2.53.0