From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f200.google.com (mail-pg1-f200.google.com [209.85.215.200]) (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 211D147A0A9 for ; Wed, 26 Aug 2026 16:42:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.200 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787762557; cv=none; b=Z7y9GjSfdpbPaxz9Z6cgbEGzJy9Xw0JQF2SwS3jgOQaes2YzHzkEQN9xWdmUFzipPTinDXBeNRCCL4Ux1WRcC/VUb4W1R9cKHPFxArfqLx0FQAvwQ6ROxJhiSyQX5khQK+ScwjJF5BADCeK/hE35lojvA9F7u2tgCP9GqSakYhc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787762557; c=relaxed/simple; bh=i578dgYavrIdohpu+SpEj4jJ+sVyZzrBwA5orlX4/TM=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=LmH1hDNcK4FLXe+KTYArf8yfyeTPjkx9xvR7HepSfrIyYw0rQxSq15lXqwe7XfCsaIlbXvU+ufrcXjItXoS1L9IeKBgWTGqnP5ZyKlNOJA3r72yCSzzLKQ8uJz1ZJqm/s68KARBojTOPPQrx0m22IJ1nBQSn5J3b6WwSCBFlrmo= 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=dQJ7TW0d; arc=none smtp.client-ip=209.85.215.200 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="dQJ7TW0d" Received: by mail-pg1-f200.google.com with SMTP id 41be03b00d2f7-cc1bbd7d6e6so1345109a12.3 for ; Wed, 26 Aug 2026 09:42:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1787762537; x=1788367337; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:reply-to:from:to:cc:subject:date:message-id :reply-to:content-type; bh=t27G+87/xldPf9EXxl/42NH6liZLtdScRqOAABQHwp0=; b=dQJ7TW0dItjw4PhJful09lq7CNsUAg37JXrX5Mv6wAy5X5qo8zYd4swK/euFAo6427 HaWktrz6hkFNFi8B8RK/RKq0Zt+eQbZ86iuK5U82yyVCFDZLcC1DH4ZLsnwypzhCB4y1 b4bf/dPURgM800Z5k74ji0SNwU+e6ks9yYDUWrHlMLDOXa7RaJHDLu6DstVBobkrJciM 9F/RIM2mH0zELbGYWaJrd4kCZZ+R8cWoAB7YlaZKrHsTEeIhqvQ6dtHN/EoSwkYLGw1d jF3uKo1e5qPZy4pptOOVRflIvgJ5dEFtoNt/VFqDiGexxEg/GsaZYXKiSInzFUMhRPu2 zb5A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1787762538; x=1788367338; h=content-type: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:content-type; bh=t27G+87/xldPf9EXxl/42NH6liZLtdScRqOAABQHwp0=; b=d4a1CZLfzGgjPrwpFlBSoQySeiV5xBuWMFNSPH8yD0FJmtTLysk2QzHP6n0INMXL4X 5B34cE6ySg49STsAeta2VN6jRUUCMyB6Ph7XgDtDDt/RkcJi7BUjiYVDKUQbwZz4dTXK K8zNFMGtZVx9wT/3NjnfMDgLxarNmUnDmfhrCiGR+LNNhWORtDHgZOn/ExgjUqv6uAQj wmuEbMI0iaOUXYAXU2fQaWN4VqNGKT7XMvUxXgnSNOarUvH9fkowojHkk3+VeHORf7S4 lpNgyLRJZ2KVnAKj+CETxko1VnbiIJnnqoDLdx/dPnNO8hupaC4Bfz8FFn2H2kNI4mvc cCYg== X-Gm-Message-State: AFuF++l7jDZEQ2HAwDycv67/wdJ5PU/dbM2MSyUa6Z4BmkefQEARrlj5 xg1jvhbPTeFLhW7LuLIcz7FLPD0ub0r23oBE3GlQXRkHkLx/EoXciP8+l2/z20/3C0hx3PYs+IR XsEkYiw== X-Received: from pghp20.prod.google.com ([2002:a63:fe14:0:b0:c9a:c533:8316]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:4f92:b0:848:2e3c:9955 with SMTP id d2e1a72fcca58-85371fa599amr14451999b3a.4.1787762537296; Wed, 26 Aug 2026 09:42:17 -0700 (PDT) Reply-To: Sean Christopherson Date: Wed, 26 Aug 2026 09:42:11 -0700 In-Reply-To: <20260826164214.756512-1-seanjc@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260826164214.756512-1-seanjc@google.com> X-Mailer: git-send-email 2.55.0.860.g4b6b3295ed-goog Message-ID: <20260826164214.756512-2-seanjc@google.com> Subject: [PATCH v2 1/4] KVM: x86/mmu: Reload MMU on *every* page pre-fault attempt/iteration From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Rick Edgecombe , Kai Huang , Yan Zhao , Sashiko Bot Content-Type: text/plain; charset="UTF-8" Reload the MMU (which is a nop if the MMU doesn't need to be reloaded) on every attempt to pre-fault a guest page, i.e. when the page fault path signals that the caller should retry. If the synchronize_srcu_expedited() in kvm_invalidate_memslot() completes before kvm_vcpu_pre_fault_memory() grabs SRCU, but kvm_mmu_reload() in the pre-fault path completes before kvm_invalidate_memslot() triggers x86's "fast zap all", then the pre-fault task will reach kvm_tdp_page_prefault() with an invalid root. Attempting to fault-in memory with an invalid root ultimately puts kvm_tdp_page_prefault() into an infinite (breakable) retry loop, which manifests most obviously as a hang in the pre_fault_memory_test selftest, but also eventually causes RCU (SRCU?) to complain. INFO: rcu_tasks detected stalls on tasks: 000000000cda47bd: .. nvcsw: 6/6 holdout: 1 idle_cpu: -1/25 task:pre_fault_memor state:R running task stack:12696 pid:95588 tgid:95588 ppid:95584 task_flags:0x400000 flags:0x00080801 Call Trace: lock_release+0x4e/0x320 __get_user_pages+0x546/0xcd0 up_read+0x1b/0x30 get_user_pages_unlocked+0xee/0x350 hva_to_pfn+0xd3/0x3d0 [kvm] lock_release+0x4e/0x320 xa_load+0x5c/0x170 xa_load+0x14c/0x170 __kvm_faultin_pfn+0xd9/0x130 [kvm] lock_acquire+0x65/0x2b0 lock_release+0x4e/0x320 kvm_mmu_faultin_pfn+0x1e1/0x690 [kvm] gup_fast_fallback+0x63e/0xdf0 kvm_tdp_page_fault+0xeb/0x140 [kvm] kvm_mmu_do_page_fault+0x12e/0x200 [kvm] kvm_arch_vcpu_pre_fault_memory+0x16e/0x200 [kvm] kvm_vcpu_pre_fault_memory+0xc1/0x1f0 [kvm] kvm_vcpu_pre_fault_memory+0x116/0x1f0 [kvm] kvm_vcpu_ioctl+0x3a4/0x6b0 [kvm] clockevents_program_event+0x5d/0x170 __se_sys_ioctl+0x6d/0xb0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 do_syscall_64+0x10a/0x480 __irq_exit_rcu+0x8e/0x140 entry_SYSCALL_64_after_hwframe+0x4b/0x53 Fixes: 6e01b7601dfe ("KVM: x86: Implement kvm_arch_vcpu_pre_fault_memory()") Reviewed-by: Rick Edgecombe Reviewed-by: Kai Huang Signed-off-by: Sean Christopherson --- arch/x86/kvm/mmu/mmu.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 064ecc33b926..3220f05387b5 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -5061,6 +5061,10 @@ static int kvm_tdp_page_prefault(struct kvm_vcpu *vcpu, gpa_t gpa, if (kvm_check_request(KVM_REQ_VM_DEAD, vcpu)) return -EIO; + r = kvm_mmu_reload(vcpu); + if (r) + return r; + cond_resched(); r = kvm_mmu_do_page_fault(vcpu, gpa, error_code, true, NULL, level); } while (r == RET_PF_RETRY); @@ -5101,14 +5105,6 @@ long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu, if (kvm_is_gfn_alias(vcpu->kvm, gpa_to_gfn(range->gpa))) return -EINVAL; - /* - * reload is efficient when called repeatedly, so we can do it on - * every iteration. - */ - r = kvm_mmu_reload(vcpu); - if (r) - return r; - direct_bits = 0; if (kvm_arch_has_private_mem(vcpu->kvm) && kvm_mem_is_private(vcpu->kvm, gpa_to_gfn(range->gpa))) -- 2.55.0.860.g4b6b3295ed-goog