From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 662FD2054EF; Thu, 12 Dec 2024 16:37:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734021461; cv=none; b=SHs4rTMc/NIvYvgQkKPigZPgawP4GOJHApZbi21HaNItP7vceVkWs7X/FN9LlYxU2ttFJyVepTktxQJzlAXBumNj9UYEnfvOLuBwyey7A+mwHds9iYn36wQKkvvzYqz8HJyxQ5ffjAKIBLyr/WdP+DOGpur6RmaMG6VXy4m7vwY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734021461; c=relaxed/simple; bh=oDz54dkru8uxY8MigODuxHkeXkhi2CPJoADuUP3ECp0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=d34R0BKag9k+icJWGNF9ky2r6mksgU/0sWJEd4hwXyV2poztQ1DAgrAUboB6TljH6CfhmjtUdgIno1CjKz0wBxqt5tcMS9TLCe7vFmufkBaL5Cp6foJRrJigr6qOzy2w6uJzeaVynI1Dv+Sa8vkyKr13pSPZGYWHmtWDsSS9WC0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Hfl8ZZAA; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Hfl8ZZAA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B1704C4CECE; Thu, 12 Dec 2024 16:37:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1734021461; bh=oDz54dkru8uxY8MigODuxHkeXkhi2CPJoADuUP3ECp0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Hfl8ZZAA5AUAgXFmimx0Oeb8mlUr61YFJyxGt3LTAqqUpCO3xU9nPn2NUw92jDdzJ bafmRqrbqQ2o7TJwT6c01rZQnZ51naHV4Gna3zRftShn/llWEJL6vFsnHMv7t0Yd1t U7C1/0/4+Ejx/SXjJXe2gg1BJ7cmdZGJ/P6YMJMM= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Sean Christopherson , Nikolay Kuratov Subject: [PATCH 6.1 742/772] KVM: x86/mmu: Ensure that kvm_release_pfn_clean() takes exact pfn from kvm_faultin_pfn() Date: Thu, 12 Dec 2024 16:01:27 +0100 Message-ID: <20241212144420.595677651@linuxfoundation.org> X-Mailer: git-send-email 2.47.1 In-Reply-To: <20241212144349.797589255@linuxfoundation.org> References: <20241212144349.797589255@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Nikolay Kuratov Since 5.16 and prior to 6.13 KVM can't be used with FSDAX guest memory (PMD pages). To reproduce the issue you need to reserve guest memory with `memmap=` cmdline, create and mount FS in DAX mode (tested both XFS and ext4), see doc link below. ndctl command for test: ndctl create-namespace -v -e namespace1.0 --map=dev --mode=fsdax -a 2M Then pass memory object to qemu like: -m 8G -object memory-backend-file,id=ram0,size=8G,\ mem-path=/mnt/pmem/guestmem,share=on,prealloc=on,dump=off,align=2097152 \ -numa node,memdev=ram0,cpus=0-1 QEMU fails to run guest with error: kvm run failed Bad address and there are two warnings in dmesg: WARN_ON_ONCE(!page_count(page)) in kvm_is_zone_device_page() and WARN_ON_ONCE(folio_ref_count(folio) <= 0) in try_grab_folio() (v6.6.63) It looks like in the past assumption was made that pfn won't change from faultin_pfn() to release_pfn_clean(), e.g. see commit 4cd071d13c5c ("KVM: x86/mmu: Move calls to thp_adjust() down a level") But kvm_page_fault structure made pfn part of mutable state, so now release_pfn_clean() can take hugepage-adjusted pfn. And it works for all cases (/dev/shm, hugetlb, devdax) except fsdax. Apparently in fsdax mode faultin-pfn and adjusted-pfn may refer to different folios, so we're getting get_page/put_page imbalance. To solve this preserve faultin pfn in separate local variable and pass it in kvm_release_pfn_clean(). Patch tested for all mentioned guest memory backends with tdp_mmu={0,1}. No bug in upstream as it was solved fundamentally by commit 8dd861cc07e2 ("KVM: x86/mmu: Put refcounted pages instead of blindly releasing pfns") and related patch series. Link: https://nvdimm.docs.kernel.org/2mib_fs_dax.html Fixes: 2f6305dd5676 ("KVM: MMU: change kvm_tdp_mmu_map() arguments to kvm_page_fault") Co-developed-by: Sean Christopherson Signed-off-by: Sean Christopherson Reviewed-by: Sean Christopherson Signed-off-by: Nikolay Kuratov Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/mmu/mmu.c | 5 ++++- arch/x86/kvm/mmu/paging_tmpl.h | 5 ++++- 2 files changed, 8 insertions(+), 2 deletions(-) --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4245,6 +4245,7 @@ static int direct_page_fault(struct kvm_ bool is_tdp_mmu_fault = is_tdp_mmu(vcpu->arch.mmu); unsigned long mmu_seq; + kvm_pfn_t orig_pfn; int r; fault->gfn = fault->addr >> PAGE_SHIFT; @@ -4272,6 +4273,8 @@ static int direct_page_fault(struct kvm_ if (r != RET_PF_CONTINUE) return r; + orig_pfn = fault->pfn; + r = RET_PF_RETRY; if (is_tdp_mmu_fault) @@ -4296,7 +4299,7 @@ out_unlock: read_unlock(&vcpu->kvm->mmu_lock); else write_unlock(&vcpu->kvm->mmu_lock); - kvm_release_pfn_clean(fault->pfn); + kvm_release_pfn_clean(orig_pfn); return r; } --- a/arch/x86/kvm/mmu/paging_tmpl.h +++ b/arch/x86/kvm/mmu/paging_tmpl.h @@ -790,6 +790,7 @@ FNAME(is_self_change_mapping)(struct kvm static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault) { struct guest_walker walker; + kvm_pfn_t orig_pfn; int r; unsigned long mmu_seq; bool is_self_change_mapping; @@ -868,6 +869,8 @@ static int FNAME(page_fault)(struct kvm_ walker.pte_access &= ~ACC_EXEC_MASK; } + orig_pfn = fault->pfn; + r = RET_PF_RETRY; write_lock(&vcpu->kvm->mmu_lock); @@ -881,7 +884,7 @@ static int FNAME(page_fault)(struct kvm_ out_unlock: write_unlock(&vcpu->kvm->mmu_lock); - kvm_release_pfn_clean(fault->pfn); + kvm_release_pfn_clean(orig_pfn); return r; }