From: Tycho Andersen <tycho@docker.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Yisheng Xie <xieyisheng1@huawei.com>,
Juerg Haefliger <juerg.haefliger@canonical.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
kernel-hardening@lists.openwall.com,
Marco Benatto <marco.antonio.780@gmail.com>,
x86@kernel.org
Subject: Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO)
Date: Wed, 20 Sep 2017 18:02:10 -0600 [thread overview]
Message-ID: <20170921000210.drjiywtp4n75yovk@docker> (raw)
In-Reply-To: <91923595-7f02-3be0-9c59-9c1fd20c82a8@intel.com>
On Wed, Sep 20, 2017 at 04:46:41PM -0700, Dave Hansen wrote:
> On 09/12/2017 11:13 AM, Tycho Andersen wrote:
> > -void xpfo_alloc_pages(struct page *page, int order, gfp_t gfp)
> > +void xpfo_alloc_pages(struct page *page, int order, gfp_t gfp, bool will_map)
> > {
> > int i, flush_tlb = 0;
> > struct xpfo *xpfo;
> > @@ -116,8 +116,14 @@ void xpfo_alloc_pages(struct page *page, int order, gfp_t gfp)
> > * Tag the page as a user page and flush the TLB if it
> > * was previously allocated to the kernel.
> > */
> > - if (!test_and_set_bit(XPFO_PAGE_USER, &xpfo->flags))
> > + bool was_user = !test_and_set_bit(XPFO_PAGE_USER,
> > + &xpfo->flags);
> > +
> > + if (was_user || !will_map) {
> > + set_kpte(page_address(page + i), page + i,
> > + __pgprot(0));
> > flush_tlb = 1;
> > + }
>
> Shouldn't the "was_user" be "was_kernel"?
Oof, yes, thanks.
> Also, the way this now works, let's say we have a nice, 2MB pmd_t (page
> table entry) mapping a nice, 2MB page in the allocator. Then it gets
> allocated to userspace. We do
>
> for (i = 0; i < (1 << order); i++) {
> ...
> set_kpte(page_address(page + i), page+i, __pgprot(0));
> }
>
> The set_kpte() will take the nice, 2MB mapping and break it down into
> 512 4k mappings, all pointing to a non-present PTE, in a newly-allocated
> PTE page. So, you get the same result and waste 4k of memory in the
> process, *AND* make it slower because we added a level to the page tables.
>
> I think you actually want to make a single set_kpte() call at the end of
> the function. That's faster and preserves the large page in the direct
> mapping.
...and makes it easier to pair tlb flushes with changing the
protections. I guess we still need the for loop, because we need to
set/unset the xpfo bits as necessary, but I'll switch it to a single
set_kpte(). This also implies that the xpfo bits should all be the
same on every page in the mapping, which I think is true.
This will be a nice change, thanks!
Tycho
next prev parent reply other threads:[~2017-09-21 0:02 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-07 17:35 [PATCH v6 00/11] Add support for eXclusive Page Frame Ownership Tycho Andersen
2017-09-07 17:35 ` [PATCH v6 01/11] mm: add MAP_HUGETLB support to vm_mmap Tycho Andersen
2017-09-08 7:42 ` Christoph Hellwig
2017-09-07 17:36 ` [PATCH v6 02/11] x86: always set IF before oopsing from page fault Tycho Andersen
2017-09-07 17:36 ` [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) Tycho Andersen
2017-09-07 18:33 ` Ralph Campbell
2017-09-07 18:50 ` Tycho Andersen
2017-09-08 7:51 ` Christoph Hellwig
2017-09-08 14:58 ` Tycho Andersen
2017-09-09 15:35 ` Laura Abbott
2017-09-11 15:03 ` Tycho Andersen
2017-09-11 7:24 ` Yisheng Xie
2017-09-11 14:50 ` Tycho Andersen
2017-09-11 16:03 ` Juerg Haefliger
2017-09-11 16:59 ` Tycho Andersen
2017-09-12 8:05 ` Yisheng Xie
2017-09-12 14:36 ` Tycho Andersen
2017-09-12 18:13 ` Tycho Andersen
2017-09-14 6:15 ` Yisheng Xie
2017-09-20 23:46 ` Dave Hansen
2017-09-21 0:02 ` Tycho Andersen [this message]
2017-09-21 0:04 ` Dave Hansen
2017-09-11 18:32 ` Tycho Andersen
2017-09-11 21:54 ` Marco Benatto
2017-09-20 15:48 ` Dave Hansen
2017-09-20 22:34 ` Tycho Andersen
2017-09-20 23:21 ` Dave Hansen
2017-09-21 0:09 ` Tycho Andersen
2017-09-21 0:27 ` Dave Hansen
2017-09-21 1:37 ` Tycho Andersen
2017-11-10 1:09 ` Tycho Andersen
2017-11-13 22:20 ` Dave Hansen
2017-11-13 22:46 ` Dave Hansen
2017-11-15 0:33 ` [kernel-hardening] " Tycho Andersen
2017-11-15 0:37 ` Dave Hansen
2017-11-15 0:42 ` Tycho Andersen
2017-11-15 3:44 ` Matthew Wilcox
2017-11-15 7:00 ` Dave Hansen
2017-11-15 14:58 ` Matthew Wilcox
2017-11-15 16:20 ` [kernel-hardening] " Tycho Andersen
2017-11-15 21:34 ` Matthew Wilcox
2017-09-21 0:03 ` Dave Hansen
2017-09-21 0:28 ` Dave Hansen
2017-09-21 1:04 ` Tycho Andersen
2017-09-07 17:36 ` [PATCH v6 04/11] swiotlb: Map the buffer if it was unmapped by XPFO Tycho Andersen
2017-09-07 18:10 ` Christoph Hellwig
2017-09-07 18:44 ` Tycho Andersen
2017-09-08 7:13 ` Christoph Hellwig
2017-09-07 17:36 ` [PATCH v6 05/11] arm64/mm: Add support for XPFO Tycho Andersen
2017-09-08 7:53 ` Christoph Hellwig
2017-09-08 17:24 ` Tycho Andersen
2017-09-14 10:41 ` Julien Grall
2017-09-14 11:29 ` Juergen Gross
2017-09-14 18:22 ` [kernel-hardening] " Mark Rutland
2017-09-18 21:27 ` Tycho Andersen
2017-09-07 17:36 ` [PATCH v6 06/11] xpfo: add primitives for mapping underlying memory Tycho Andersen
2017-09-07 17:36 ` [PATCH v6 07/11] arm64/mm, xpfo: temporarily map dcache regions Tycho Andersen
2017-09-14 18:25 ` Mark Rutland
2017-09-18 21:29 ` Tycho Andersen
2017-09-07 17:36 ` [PATCH v6 08/11] arm64/mm: Add support for XPFO to swiotlb Tycho Andersen
2017-09-07 17:36 ` [PATCH v6 09/11] arm64/mm: disable section/contiguous mappings if XPFO is enabled Tycho Andersen
2017-09-09 15:38 ` Laura Abbott
2017-09-07 17:36 ` [PATCH v6 10/11] mm: add a user_virt_to_phys symbol Tycho Andersen
2017-09-08 7:55 ` Christoph Hellwig
2017-09-08 15:44 ` Kees Cook
2017-09-11 7:36 ` Christoph Hellwig
2017-09-14 18:34 ` [kernel-hardening] " Mark Rutland
2017-09-18 20:56 ` Tycho Andersen
2017-09-07 17:36 ` [PATCH v6 11/11] lkdtm: Add test for XPFO Tycho Andersen
2017-09-07 19:08 ` Kees Cook
2017-09-10 0:57 ` kbuild test robot
2017-09-11 10:34 ` [PATCH v6 00/11] Add support for eXclusive Page Frame Ownership Yisheng Xie
2017-09-11 15:02 ` Tycho Andersen
2017-09-12 7:07 ` Yisheng Xie
2017-09-12 7:40 ` Juerg Haefliger
2017-09-12 8:11 ` Yisheng Xie
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