From nobody Thu Oct 9 14:46:09 2025 Received: from mail-pl1-f201.google.com (mail-pl1-f201.google.com [209.85.214.201]) (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 D0D9420E6F9 for ; Wed, 18 Jun 2025 04:24:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750220677; cv=none; b=RT0125zb9DIEvgpo+NfHe8rgUeWgI2bpyIG2yzeupB/JdetG0cWZhLoZ9JNCV+CWeZPE/O3d5zVV3EnggTzuHlOq5KdYdeUzR+8HiSnRf5lg2gZGaTjtfL9VjW21b96Vk2z2njc1dNtJLHfy1Rszkfg0yT+k/Vmv8HrITEhiYJg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750220677; c=relaxed/simple; bh=Fd4SdpBpGMWqTpDQtVvgHQNQARLYxNkES4VtDZAj2OE=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=d0WpxL0+yWif5nrDflsQjIjlEEnrPFQngnnPcLjdI4vIrpLiCrQE9gPHS2LmrSlfu6M111VE0EN4iRFuzGLDGuTeHKx/LCMFfXmMqr/PG9fDAKA9CHnhZb9Wh2vUWtQEwl1eZ2H4K4aRTzh+dWcs5HD8gXZvw/ayNUSIRABu/wE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--jthoughton.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=KH1B+lap; arc=none smtp.client-ip=209.85.214.201 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--jthoughton.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="KH1B+lap" Received: by mail-pl1-f201.google.com with SMTP id d9443c01a7336-235f6b829cfso51739775ad.2 for ; Tue, 17 Jun 2025 21:24:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1750220675; x=1750825475; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=He9GMZwZGhbuABKsoN3wz9xUeb4JLf+qOIjtO6Uhl9c=; b=KH1B+laphzq9ggMTEQZDW66kmcpSWnAYBsc+aRZHqDzrFFdd5a2kfuMyA8Do5iKMKK TNM2qWwAsbo54UwgRLqPmu9xIm6uchA7dv8+Lifren1AYDWH26/xsEBFRfxGw1Rxrv0E RtugHExSRwAyTo5Rw3URXCtupYMjsnTcre+cWu3ud2Axr7N0TOxsA7URRl7vt4QM3ldj +5NTxYki7ofVN0hAqzgKWbzYtezZJHziPrYJ+1TiySFeURxabaBEE7o+XX5NW2vS9Yjw 8XjGR4lcCmA9ZcuRj+7D4fRxXBEnoPaaqVSGa4pn0EwgXRVDp66lbSu9X4sMFXNJpbas lx7g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1750220675; x=1750825475; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=He9GMZwZGhbuABKsoN3wz9xUeb4JLf+qOIjtO6Uhl9c=; b=eMqyzFpLbwY3coZy7h+nLQJacnRp1YranJRSrurLVO7c0HBz7sQcZdGc6BPzuDrqtc RQAW3adsBz29LIs0KXpYCI13UAZ+Bz2Yx04F17OlczzB8K/tiLCCMx1g/KstQYGg+FmT aOPGAqb9gPqz6wxrxS0+8wxQJ+fVLbVT8gcCBhatP5TI1F5YtJi0Fgr9woXQGFXVOyRr /1J3T86/XZH2rGN0Bo0Rhgbo7TGjfoGCMmZuCeETZ6ypnuqeF+WarWcs4y7nGJGqhGbb oKdTLD99cum9xw7ItNTXo1NTitlKr3gK2jJnyKYduH8u1pS3HOvwU9tO2IKjVzKQOy0f NTSg== X-Forwarded-Encrypted: i=1; AJvYcCXh8EAvniXwpnZIEOdKRbQg5jsQM4sOaNhF5oVUaal6tuv47IMhPoA2BJPqWRKEmfguAWQJx8ZOwy4p9wM=@vger.kernel.org X-Gm-Message-State: AOJu0YzAERkHiiMBTgq3v4KfXeuD7PytcYzq9WtMN01S5MWLA7tK2Q2c +mBHuDM4VgLtK1A5kHsT/QIDJXLqKujLQMCRMVtZy8scMrX7NNUF3Y3+/UDEsJjPZGmtlL2KBQq n5JHelO4yZA0GbdX2W6H2Fw== X-Google-Smtp-Source: AGHT+IEz+sYmwmOj4IeHxcE6XX3uQvv4AyNEb1cpKl7A16mtz5cSX2RNnd2uZJbF+w+tZiQScGXmjNJtGrMaKECU X-Received: from pjtd15.prod.google.com ([2002:a17:90b:4f:b0:30a:31eb:ec8e]) (user=jthoughton job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:dacc:b0:234:c8f6:1b05 with SMTP id d9443c01a7336-2366b3fe725mr232646505ad.52.1750220674878; Tue, 17 Jun 2025 21:24:34 -0700 (PDT) Date: Wed, 18 Jun 2025 04:24:14 +0000 In-Reply-To: <20250618042424.330664-1-jthoughton@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250618042424.330664-1-jthoughton@google.com> X-Mailer: git-send-email 2.50.0.rc2.696.g1fc2a0284f-goog Message-ID: <20250618042424.330664-6-jthoughton@google.com> Subject: [PATCH v3 05/15] KVM: x86: Add support for KVM userfault exits From: James Houghton To: Paolo Bonzini , Sean Christopherson , Oliver Upton Cc: Jonathan Corbet , Marc Zyngier , Yan Zhao , James Houghton , Nikita Kalyazin , Anish Moorthy , Peter Gonda , Peter Xu , David Matlack , wei.w.wang@intel.com, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Only a few changes are needed to support KVM userfault exits on x86: 1. Adjust kvm_mmu_hugepage_adjust() to force pages to be mapped at 4K while KVM_MEM_USERFAULT is enabled. 2. Return -EFAULT when kvm_do_userfault() when it reports that the page is userfault. (Upon failure to read from the bitmap, kvm_do_userfault() will return true without setting up a memory fault exit, so we'll return a bare -EFAULT). For hugepage recovery, the behavior when disabling KVM_MEM_USERFAULT should match the behavior when disabling KVM_MEM_LOG_DIRTY_PAGES; make changes to kvm_mmu_slot_apply_flags() to recover hugepages when KVM_MEM_USERFAULT is disabled. Signed-off-by: James Houghton Signed-off-by: Sean Christopherson --- arch/x86/kvm/mmu/mmu.c | 5 ++++- arch/x86/kvm/x86.c | 27 +++++++++++++++++---------- 2 files changed, 21 insertions(+), 11 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index a4439e9e07268..49eb6b9b268cb 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -3304,7 +3304,7 @@ void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, s= truct kvm_page_fault *fault if (is_error_noslot_pfn(fault->pfn)) return; =20 - if (kvm_slot_dirty_track_enabled(slot)) + if (kvm_slot_dirty_track_enabled(slot) || kvm_is_userfault_memslot(slot)) return; =20 /* @@ -4522,6 +4522,9 @@ static int __kvm_mmu_faultin_pfn(struct kvm_vcpu *vcp= u, { unsigned int foll =3D fault->write ? FOLL_WRITE : 0; =20 + if (kvm_do_userfault(vcpu, fault)) + return -EFAULT; + if (fault->is_private) return kvm_mmu_faultin_pfn_private(vcpu, fault); =20 diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index b58a74c1722de..fa279ba38115c 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -13152,12 +13152,27 @@ static void kvm_mmu_slot_apply_flags(struct kvm *= kvm, u32 new_flags =3D new ? new->flags : 0; bool log_dirty_pages =3D new_flags & KVM_MEM_LOG_DIRTY_PAGES; =20 + /* + * Recover hugepages when userfault is toggled off, as KVM forces 4KiB + * mappings when userfault is enabled. See below for why CREATE, MOVE, + * and DELETE don't need special handling. Note, common KVM handles + * zapping SPTEs when userfault is toggled on. + */ + if (change =3D=3D KVM_MR_FLAGS_ONLY && (old_flags & KVM_MEM_USERFAULT) && + !(new_flags & KVM_MEM_USERFAULT)) + kvm_mmu_recover_huge_pages(kvm, new); + + /* + * Nothing more to do if dirty logging isn't being toggled. + */ + if (!((old_flags ^ new_flags) & KVM_MEM_LOG_DIRTY_PAGES)) + return; + /* * Update CPU dirty logging if dirty logging is being toggled. This * applies to all operations. */ - if ((old_flags ^ new_flags) & KVM_MEM_LOG_DIRTY_PAGES) - kvm_mmu_update_cpu_dirty_logging(kvm, log_dirty_pages); + kvm_mmu_update_cpu_dirty_logging(kvm, log_dirty_pages); =20 /* * Nothing more to do for RO slots (which can't be dirtied and can't be @@ -13177,14 +13192,6 @@ static void kvm_mmu_slot_apply_flags(struct kvm *k= vm, if ((change !=3D KVM_MR_FLAGS_ONLY) || (new_flags & KVM_MEM_READONLY)) return; =20 - /* - * READONLY and non-flags changes were filtered out above, and the only - * other flag is LOG_DIRTY_PAGES, i.e. something is wrong if dirty - * logging isn't being toggled on or off. - */ - if (WARN_ON_ONCE(!((old_flags ^ new_flags) & KVM_MEM_LOG_DIRTY_PAGES))) - return; - if (!log_dirty_pages) { /* * Recover huge page mappings in the slot now that dirty logging --=20 2.50.0.rc2.692.g299adb8693-goog