From owner-dev-commits-src-main@freebsd.org Thu Jul 22 19:04:23 2021 Return-Path: Delivered-To: dev-commits-src-main@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 019A166440A; Thu, 22 Jul 2021 19:04:23 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "R3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4GW21f6Dc3z4q9C; Thu, 22 Jul 2021 19:04:22 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org (gitrepo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id BDA4717581; Thu, 22 Jul 2021 19:04:22 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org ([127.0.1.44]) by gitrepo.freebsd.org (8.16.1/8.16.1) with ESMTP id 16MJ4MeI039773; Thu, 22 Jul 2021 19:04:22 GMT (envelope-from git@gitrepo.freebsd.org) Received: (from git@localhost) by gitrepo.freebsd.org (8.16.1/8.16.1/Submit) id 16MJ4M6S039772; Thu, 22 Jul 2021 19:04:22 GMT (envelope-from git) Date: Thu, 22 Jul 2021 19:04:22 GMT Message-Id: <202107221904.16MJ4M6S039772@gitrepo.freebsd.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org From: Jessica Clarke Subject: git: 4a235049082e - main - riscv: Fix pmap_kextract racing with concurrent superpage promotion/demotion MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Git-Committer: jrtc27 X-Git-Repository: src X-Git-Refname: refs/heads/main X-Git-Reftype: branch X-Git-Commit: 4a235049082ee1cb044873ad9aff12cf73d0fd3b Auto-Submitted: auto-generated X-BeenThere: dev-commits-src-main@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Commit messages for the main branch of the src repository List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 22 Jul 2021 19:04:23 -0000 The branch main has been updated by jrtc27: URL: https://cgit.FreeBSD.org/src/commit/?id=4a235049082ee1cb044873ad9aff12cf73d0fd3b commit 4a235049082ee1cb044873ad9aff12cf73d0fd3b Author: Jessica Clarke AuthorDate: 2021-07-22 19:02:14 +0000 Commit: Jessica Clarke CommitDate: 2021-07-22 19:02:14 +0000 riscv: Fix pmap_kextract racing with concurrent superpage promotion/demotion This repeats amd64's cfcbf8c6fd3b (r180498) and i386's cf3508519c5e (r202894) but for riscv; pmap_kextract must be lock-free and so it can race with superpage promotion and demotion, thus the L2 entry must only be loaded once to avoid using inconsistent state. PR: 250866 Reviewed by: markj, mhorne Tested by: David Gilbert MFC after: 1 week Differential Revision: https://reviews.freebsd.org/D31253 --- sys/riscv/riscv/pmap.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/sys/riscv/riscv/pmap.c b/sys/riscv/riscv/pmap.c index 39595b10d7b2..0bb22bd13bbe 100644 --- a/sys/riscv/riscv/pmap.c +++ b/sys/riscv/riscv/pmap.c @@ -872,7 +872,7 @@ pmap_extract_and_hold(pmap_t pmap, vm_offset_t va, vm_prot_t prot) vm_paddr_t pmap_kextract(vm_offset_t va) { - pd_entry_t *l2; + pd_entry_t *l2, l2e; pt_entry_t *l3; vm_paddr_t pa; @@ -882,14 +882,23 @@ pmap_kextract(vm_offset_t va) l2 = pmap_l2(kernel_pmap, va); if (l2 == NULL) panic("pmap_kextract: No l2"); - if ((pmap_load(l2) & PTE_RX) != 0) { + l2e = pmap_load(l2); + /* + * Beware of concurrent promotion and demotion! We must + * use l2e rather than loading from l2 multiple times to + * ensure we see a consistent state, including the + * implicit load in pmap_l2_to_l3. It is, however, safe + * to use an old l2e because the L3 page is preserved by + * promotion. + */ + if ((l2e & PTE_RX) != 0) { /* superpages */ - pa = L2PTE_TO_PHYS(pmap_load(l2)); + pa = L2PTE_TO_PHYS(l2e); pa |= (va & L2_OFFSET); return (pa); } - l3 = pmap_l2_to_l3(l2, va); + l3 = pmap_l2_to_l3(&l2e, va); if (l3 == NULL) panic("pmap_kextract: No l3..."); pa = PTE_TO_PHYS(pmap_load(l3));