From patchwork Thu Jun 20 00:53:33 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Jason A. Donenfeld" X-Patchwork-Id: 13704783 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id B06F6C27C53 for ; Thu, 20 Jun 2024 00:54:05 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 19A7C8D0094; Wed, 19 Jun 2024 20:54:05 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 14AA08D0091; Wed, 19 Jun 2024 20:54:05 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id F2C818D0094; Wed, 19 Jun 2024 20:54:04 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id D21498D0091 for ; Wed, 19 Jun 2024 20:54:04 -0400 (EDT) Received: from smtpin07.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 695D1A15A8 for ; Thu, 20 Jun 2024 00:54:04 +0000 (UTC) X-FDA: 82249445208.07.5ECFAD8 Received: from sin.source.kernel.org (sin.source.kernel.org [145.40.73.55]) by imf08.hostedemail.com (Postfix) with ESMTP id E06C2160008 for ; Thu, 20 Jun 2024 00:54:01 +0000 (UTC) Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=zx2c4.com header.s=20210105 header.b=Wy1GiSRp; spf=pass (imf08.hostedemail.com: domain of "SRS0=6i12=NW=zx2c4.com=Jason@kernel.org" designates 145.40.73.55 as permitted sender) smtp.mailfrom="SRS0=6i12=NW=zx2c4.com=Jason@kernel.org"; dmarc=pass (policy=quarantine) header.from=zx2c4.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1718844836; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=HIMpXESIZrvLDlNkbefExpVi2+GH2WoPeJxzWPkZD3s=; b=zpkAajkSKtuNIq8KanjKbr2HwfXC1nvp1Cst+sf9dsEu2yTrjawyG9/jbeEQ4aneLjJ4Yi KFqijh7dUWbnSQWIvZZO6XhtRhL5p1L10Es57CL6Bh7NE1wXcXV1WKC/h+s6kqK05E7SP9 FANv0RkBSPDxvJpqp8MAYAn/5c8+LtM= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=zx2c4.com header.s=20210105 header.b=Wy1GiSRp; spf=pass (imf08.hostedemail.com: domain of "SRS0=6i12=NW=zx2c4.com=Jason@kernel.org" designates 145.40.73.55 as permitted sender) smtp.mailfrom="SRS0=6i12=NW=zx2c4.com=Jason@kernel.org"; dmarc=pass (policy=quarantine) header.from=zx2c4.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1718844836; a=rsa-sha256; cv=none; b=C5xeMA5rlF8k5FBlWZXzcqVgyexEropPJJbSiNEaAtxXwTqOWZmf1bhU8faxyzXsnD363p lPPcwKNt6I6Sq+Am8JTa6pYKImbwuqr6m3X+xdC+KAcqVl1JtYBp67nmjjBGGzKqC2iCu5 B5wYuayvvigM+x92C7CzN2Gv3Zq6IDA= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sin.source.kernel.org (Postfix) with ESMTP id D5784CE22C6; Thu, 20 Jun 2024 00:53:58 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CCE43C4AF07; Thu, 20 Jun 2024 00:53:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1718844836; 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=HIMpXESIZrvLDlNkbefExpVi2+GH2WoPeJxzWPkZD3s=; b=Wy1GiSRpjhNsHn9qVAbJoz3aTmgx+UwkCBCrXvetGSx0fpRQggPQJeiKHmKHETFO+pAPSy z0tr/DVKQCuWhqUgE9gKabZy9rhUMCnaJNxaCOK5tinl4kycBw/hJRHI19NsFDExBjqUaF MmaFuD/ddGMWswF63lXcs2l49f+hjPo= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id a4359615 (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Thu, 20 Jun 2024 00:53:55 +0000 (UTC) From: "Jason A. Donenfeld" To: linux-kernel@vger.kernel.org, patches@lists.linux.dev, tglx@linutronix.de Cc: "Jason A. Donenfeld" , linux-crypto@vger.kernel.org, linux-api@vger.kernel.org, x86@kernel.org, Greg Kroah-Hartman , Adhemerval Zanella Netto , Carlos O'Donell , Florian Weimer , Arnd Bergmann , Jann Horn , Christian Brauner , David Hildenbrand , linux-mm@kvack.org Subject: [PATCH v18 1/5] mm: add VM_DROPPABLE for designating always lazily freeable mappings Date: Thu, 20 Jun 2024 02:53:33 +0200 Message-ID: <20240620005339.1273434-2-Jason@zx2c4.com> In-Reply-To: <20240620005339.1273434-1-Jason@zx2c4.com> References: <20240620005339.1273434-1-Jason@zx2c4.com> MIME-Version: 1.0 X-Stat-Signature: xpou6jjxtpzdqoyud3dpin6gs1dciy6m X-Rspam-User: X-Rspamd-Queue-Id: E06C2160008 X-Rspamd-Server: rspam02 X-HE-Tag: 1718844841-565121 X-HE-Meta: U2FsdGVkX19A/4hIWYUqiYmfAN1/v75/IjArM28dE2jSGanM0lEdrUvTs2HOt3WQOVPLv9Z7ODGENuum5d92ru7TWkvSPPY4tk5SYDpxLuiawZHBXLRHq9Oe4soO9IeD1Lf+qCTOU4MXS8JLqZxjsHz01awNZ3U3/uchR64nFW3cuFDyJQeYHF6H51/XWeDJHz45d6WQFwRjL7PeOzh9mbeMvK+te5Xjdm3Dp2kTue6sOPpedoC6vqpwodUccUAEOOYjHHeBRsm/T82GIJvs3i6Ta6YAGrTnpuDEJUsXJgKy5c9XcZaonsdGL2M5WcZia6a61kVuIAOrTPacZ2+NBmKkewwC8e159jbCKiVIw3qnZXw+PUJ3wHKXK0zXzAKz69+M4tllfVQdoU2ZfI3m85/987hmJMeXylmmzNqG8uL389ccoyhnCYv7jNhTNHzRQVIPGlP2qYqAY8+CuPsMVsg3X7Feyozbd+yWilXnUeG0O3IPyg2SReZNNyfUQAFBYXd6rX4k+1GuWtYhfPyAqR+vIZilAZ5m5o7oaDP4wP+1+rFns7PAGO7G9cPB6po9MJgU2jTwYdrAK7/bKi0qGLO1ggn3Z2QlwAybBPlIjvIuPGuWms8ZR6yPZ832vEIpytyPFLctD/SEyrWPPiMKOzrBHnMwdNxtvFbXYSjraVELuZMqyjzTulnROuBfYMjCgaxpGaTbYat/Q1+bZKoIALUjkwMcB3OdNNokEWvIPM/IvKZVSpg23UzY3U+uBk3X/xfB/cvd+jtely0mhjFMwCEZviLMbLK7rw3vpuOmyJ5v0p45aoZNFHoJcBPxu5qR4hnJZgYkHY07yehYSzqoY7vuc9TyqKgliUXo460MB/YK9OXdGUcq1+jS7nHWPFDPB8sUDW1LIwvMBGrNpG6Jg65KSxVaNNubOsYIlhL+zznNRnDKGA8maWUWegaaedXR0hr/YFrvh1V/84HlaRS EVgELXDV 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: The vDSO getrandom() implementation works with a buffer allocated with a new system call that has certain requirements: - It shouldn't be written to core dumps. * Easy: VM_DONTDUMP. - It should be zeroed on fork. * Easy: VM_WIPEONFORK. - It shouldn't be written to swap. * Uh-oh: mlock is rlimited. * Uh-oh: mlock isn't inherited by forks. It turns out that the vDSO getrandom() function has three really nice characteristics that we can exploit to solve this problem: 1) Due to being wiped during fork(), the vDSO code is already robust to having the contents of the pages it reads zeroed out midway through the function's execution. 2) In the absolute worst case of whatever contingency we're coding for, we have the option to fallback to the getrandom() syscall, and everything is fine. 3) The buffers the function uses are only ever useful for a maximum of 60 seconds -- a sort of cache, rather than a long term allocation. These characteristics mean that we can introduce VM_DROPPABLE, which has the following semantics: a) It never is written out to swap. b) Under memory pressure, mm can just drop the pages (so that they're zero when read back again). c) It is inherited by fork. d) It doesn't count against the mlock budget, since nothing is locked. This is fairly simple to implement, with the one snag that we have to use 64-bit VM_* flags, but this shouldn't be a problem, since the only consumers will probably be 64-bit anyway. This way, allocations used by vDSO getrandom() can use: VM_DROPPABLE | VM_DONTDUMP | VM_WIPEONFORK | VM_NORESERVE And there will be no problem with using memory when not in use, not wiping on fork(), coredumps, or writing out to swap. Cc: linux-mm@kvack.org Signed-off-by: Jason A. Donenfeld --- fs/proc/task_mmu.c | 3 +++ include/linux/mm.h | 8 ++++++++ include/trace/events/mmflags.h | 7 +++++++ mm/Kconfig | 3 +++ mm/mprotect.c | 2 +- mm/rmap.c | 8 +++++--- 6 files changed, 27 insertions(+), 4 deletions(-) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index f8d35f993fe5..1883d6462ca8 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -706,6 +706,9 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma) #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */ #ifdef CONFIG_X86_USER_SHADOW_STACK [ilog2(VM_SHADOW_STACK)] = "ss", +#endif +#ifdef CONFIG_NEED_VM_DROPPABLE + [ilog2(VM_DROPPABLE)] = "dp", #endif }; size_t i; diff --git a/include/linux/mm.h b/include/linux/mm.h index 9849dfda44d4..5978cb4cc21c 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -321,12 +321,14 @@ extern unsigned int kobjsize(const void *objp); #define VM_HIGH_ARCH_BIT_3 35 /* bit only usable on 64-bit architectures */ #define VM_HIGH_ARCH_BIT_4 36 /* bit only usable on 64-bit architectures */ #define VM_HIGH_ARCH_BIT_5 37 /* bit only usable on 64-bit architectures */ +#define VM_HIGH_ARCH_BIT_6 38 /* bit only usable on 64-bit architectures */ #define VM_HIGH_ARCH_0 BIT(VM_HIGH_ARCH_BIT_0) #define VM_HIGH_ARCH_1 BIT(VM_HIGH_ARCH_BIT_1) #define VM_HIGH_ARCH_2 BIT(VM_HIGH_ARCH_BIT_2) #define VM_HIGH_ARCH_3 BIT(VM_HIGH_ARCH_BIT_3) #define VM_HIGH_ARCH_4 BIT(VM_HIGH_ARCH_BIT_4) #define VM_HIGH_ARCH_5 BIT(VM_HIGH_ARCH_BIT_5) +#define VM_HIGH_ARCH_6 BIT(VM_HIGH_ARCH_BIT_6) #endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */ #ifdef CONFIG_ARCH_HAS_PKEYS @@ -357,6 +359,12 @@ extern unsigned int kobjsize(const void *objp); # define VM_SHADOW_STACK VM_NONE #endif +#ifdef CONFIG_NEED_VM_DROPPABLE +# define VM_DROPPABLE VM_HIGH_ARCH_6 +#else +# define VM_DROPPABLE VM_NONE +#endif + #if defined(CONFIG_X86) # define VM_PAT VM_ARCH_1 /* PAT reserves whole VMA at once (x86) */ #elif defined(CONFIG_PPC) diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h index e46d6e82765e..fab7848df50a 100644 --- a/include/trace/events/mmflags.h +++ b/include/trace/events/mmflags.h @@ -165,6 +165,12 @@ IF_HAVE_PG_ARCH_X(arch_3) # define IF_HAVE_UFFD_MINOR(flag, name) #endif +#ifdef CONFIG_NEED_VM_DROPPABLE +# define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name}, +#else +# define IF_HAVE_VM_DROPPABLE(flag, name) +#endif + #define __def_vmaflag_names \ {VM_READ, "read" }, \ {VM_WRITE, "write" }, \ @@ -197,6 +203,7 @@ IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY, "softdirty" ) \ {VM_MIXEDMAP, "mixedmap" }, \ {VM_HUGEPAGE, "hugepage" }, \ {VM_NOHUGEPAGE, "nohugepage" }, \ +IF_HAVE_VM_DROPPABLE(VM_DROPPABLE, "droppable" ) \ {VM_MERGEABLE, "mergeable" } \ #define show_vma_flags(flags) \ diff --git a/mm/Kconfig b/mm/Kconfig index b4cb45255a54..6cd65ea4b3ad 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -1056,6 +1056,9 @@ config ARCH_USES_HIGH_VMA_FLAGS bool config ARCH_HAS_PKEYS bool +config NEED_VM_DROPPABLE + select ARCH_USES_HIGH_VMA_FLAGS + bool config ARCH_USES_PG_ARCH_X bool diff --git a/mm/mprotect.c b/mm/mprotect.c index 8c6cd8825273..57b8dad9adcc 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -623,7 +623,7 @@ mprotect_fixup(struct vma_iterator *vmi, struct mmu_gather *tlb, may_expand_vm(mm, oldflags, nrpages)) return -ENOMEM; if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB| - VM_SHARED|VM_NORESERVE))) { + VM_SHARED|VM_NORESERVE|VM_DROPPABLE))) { charged = nrpages; if (security_vm_enough_memory_mm(mm, charged)) return -ENOMEM; diff --git a/mm/rmap.c b/mm/rmap.c index e8fc5ecb59b2..d873a3f06506 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1397,7 +1397,8 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma, VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio); VM_BUG_ON_VMA(address < vma->vm_start || address + (nr << PAGE_SHIFT) > vma->vm_end, vma); - __folio_set_swapbacked(folio); + if (!(vma->vm_flags & VM_DROPPABLE)) + __folio_set_swapbacked(folio); __folio_set_anon(folio, vma, address, true); if (likely(!folio_test_large(folio))) { @@ -1841,7 +1842,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, * plus the rmap(s) (dropped by discard:). */ if (ref_count == 1 + map_count && - !folio_test_dirty(folio)) { + (!folio_test_dirty(folio) || (vma->vm_flags & VM_DROPPABLE))) { dec_mm_counter(mm, MM_ANONPAGES); goto discard; } @@ -1851,7 +1852,8 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, * discarded. Remap the page to page table. */ set_pte_at(mm, address, pvmw.pte, pteval); - folio_set_swapbacked(folio); + if (!(vma->vm_flags & VM_DROPPABLE)) + folio_set_swapbacked(folio); ret = false; page_vma_mapped_walk_done(&pvmw); break;