From nobody Wed Nov 27 11:43:53 2024 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 C1834212D0F for ; Fri, 11 Oct 2024 10:25:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728642312; cv=none; b=I329KT18D+cwHarFHFKnLFncNduwIB358RTjFcM8VbTk4kzF+3ylga+Sp512g+GC6k8czDuSO2AzmcrpUmOmf+4/hGFhfLJ1IRENc00OY5NftlDwFW42i+33jT/DVJ/LXI/40izNxkNXICOD7WbOGoD2PjSYp76sOS+EcYDcBOs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728642312; c=relaxed/simple; bh=1C83OOgMcgqb57Ddo8ncVhTx9jAr8iuBqE28xGsal7g=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=W38vJgtJWCTsRnSgo3lrRTS9pM0oLTy8lYMElq4VA+o2fqSaVJ4x7yqBWFgR4giUr2P+8YmWgVgcDBlnxIdvxNIED8pHRKuL2IgNkZiAg3UUh34CViYclM7wW5oY/Z/b4QDy+gN+ls0+fPBvFIL+Gx4ERIW519rZXA6/T8UJdI8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=Eg0IZHMX; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Eg0IZHMX" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1728642308; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=UZ3IdlQSiC9SBRAFeIkUjQ3G20iTXPL8FgSwyp2DDL0=; b=Eg0IZHMXIT2pR11GyVUKzabwVHslxYHCT9x7YwXqKVku4WrzDVACHKWinBkKlyMrq66OJR h1TOgeQOWdsc0QLTUlc/VkJdn2SQCEOkHXI2TQsCeUscc/wzbhgZlU5KWsRmin1NqCunYu /Vu1hg5nRxeet4FwJob+8SSSQvZA3ts= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-638-AWsUiTUhPfSrctqTbSxh0w-1; Fri, 11 Oct 2024 06:25:05 -0400 X-MC-Unique: AWsUiTUhPfSrctqTbSxh0w-1 Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9D7D91955F3D; Fri, 11 Oct 2024 10:25:03 +0000 (UTC) Received: from t14s.fritz.box (unknown [10.22.80.4]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id E484D1956089; Fri, 11 Oct 2024 10:24:58 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, kvm@vger.kernel.org, David Hildenbrand , Andrew Morton , Hugh Dickins , Thomas Huth , "Matthew Wilcox (Oracle)" , Ryan Roberts , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Kefeng Wang , Leo Fu Subject: [PATCH v1 2/2] mm: don't install PMD mappings when THPs are disabled by the hw/process/vma Date: Fri, 11 Oct 2024 12:24:45 +0200 Message-ID: <20241011102445.934409-3-david@redhat.com> In-Reply-To: <20241011102445.934409-1-david@redhat.com> References: <20241011102445.934409-1-david@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 Content-Type: text/plain; charset="utf-8" We (or rather, readahead logic :) ) might be allocating a THP in the pagecache and then try mapping it into a process that explicitly disabled THP: we might end up installing PMD mappings. This is a problem for s390x KVM, which explicitly remaps all PMD-mapped THPs to be PTE-mapped in s390_enable_sie()->thp_split_mm(), before starting the VM. For example, starting a VM backed on a file system with large folios supported makes the VM crash when the VM tries accessing such a mapping using KVM. Is it also a problem when the HW disabled THP using TRANSPARENT_HUGEPAGE_UNSUPPORTED? At least on x86 this would be the case without X86_FEATURE_PSE. In the future, we might be able to do better on s390x and only disallow PMD mappings -- what s390x and likely TRANSPARENT_HUGEPAGE_UNSUPPORTED really wants. For now, fix it by essentially performing the same check as would be done in __thp_vma_allowable_orders() or in shmem code, where this works as expected, and disallow PMD mappings, making us fallback to PTE mappings. Reported-by: Leo Fu Fixes: 793917d997df ("mm/readahead: Add large folio readahead") Cc: Thomas Huth Cc: Matthew Wilcox (Oracle) Cc: Ryan Roberts Cc: Christian Borntraeger Cc: Janosch Frank Cc: Claudio Imbrenda Signed-off-by: David Hildenbrand Reviewed-by: Ryan Roberts --- mm/memory.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/mm/memory.c b/mm/memory.c index 2366578015ad..a2e501489517 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4925,6 +4925,15 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct p= age *page) pmd_t entry; vm_fault_t ret =3D VM_FAULT_FALLBACK; =20 + /* + * It is too late to allocate a small folio, we already have a large + * folio in the pagecache: especially s390 KVM cannot tolerate any + * PMD mappings, but PTE-mapped THP are fine. So let's simply refuse any + * PMD mappings if THPs are disabled. + */ + if (thp_disabled_by_hw() || vma_thp_disabled(vma, vma->vm_flags)) + return ret; + if (!thp_vma_suitable_order(vma, haddr, PMD_ORDER)) return ret; =20 --=20 2.46.1