From: Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
To: Khalid Aziz <khalid.aziz-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
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Khalid Aziz <khalid@gonehiking>
Subject: Re: [RFC PATCH v9 03/13] mm: Add support for eXclusive Page Frame Ownership (XPFO)
Date: Thu, 4 Apr 2019 09:43:23 +0200 [thread overview]
Message-ID: <20190404074323.GO4038@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <f1ac3700970365fb979533294774af0b0dd84b3b.1554248002.git.khalid.aziz-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
You must be so glad I no longer use kmap_atomic from NMI context :-)
On Wed, Apr 03, 2019 at 11:34:04AM -0600, Khalid Aziz wrote:
> +static inline void xpfo_kmap(void *kaddr, struct page *page)
> +{
> + unsigned long flags;
> +
> + if (!static_branch_unlikely(&xpfo_inited))
> + return;
> +
> + if (!PageXpfoUser(page))
> + return;
> +
> + /*
> + * The page was previously allocated to user space, so
> + * map it back into the kernel if needed. No TLB flush required.
> + */
> + spin_lock_irqsave(&page->xpfo_lock, flags);
> +
> + if ((atomic_inc_return(&page->xpfo_mapcount) == 1) &&
> + TestClearPageXpfoUnmapped(page))
> + set_kpte(kaddr, page, PAGE_KERNEL);
> +
> + spin_unlock_irqrestore(&page->xpfo_lock, flags);
That's a really sad sequence, not wrong, but sad. _3_ atomic operations,
2 on likely the same cacheline. And mostly all pointless.
This patch makes xpfo_mapcount an atomic, but then all modifications are
under the spinlock, what gives?
Anyway, a possibly saner sequence might be:
if (atomic_inc_not_zero(&page->xpfo_mapcount))
return;
spin_lock_irqsave(&page->xpfo_lock, flag);
if ((atomic_inc_return(&page->xpfo_mapcount) == 1) &&
TestClearPageXpfoUnmapped(page))
set_kpte(kaddr, page, PAGE_KERNEL);
spin_unlock_irqrestore(&page->xpfo_lock, flags);
> +}
> +
> +static inline void xpfo_kunmap(void *kaddr, struct page *page)
> +{
> + unsigned long flags;
> +
> + if (!static_branch_unlikely(&xpfo_inited))
> + return;
> +
> + if (!PageXpfoUser(page))
> + return;
> +
> + /*
> + * The page is to be allocated back to user space, so unmap it from
> + * the kernel, flush the TLB and tag it as a user page.
> + */
> + spin_lock_irqsave(&page->xpfo_lock, flags);
> +
> + if (atomic_dec_return(&page->xpfo_mapcount) == 0) {
> +#ifdef CONFIG_XPFO_DEBUG
> + WARN_ON(PageXpfoUnmapped(page));
> +#endif
> + SetPageXpfoUnmapped(page);
> + set_kpte(kaddr, page, __pgprot(0));
> + xpfo_flush_kernel_tlb(page, 0);
You didn't speak about the TLB invalidation anywhere. But basically this
is one that x86 cannot do.
> + }
> +
> + spin_unlock_irqrestore(&page->xpfo_lock, flags);
Idem:
if (atomic_add_unless(&page->xpfo_mapcount, -1, 1))
return;
....
> +}
Also I'm failing to see the point of PG_xpfo_unmapped, afaict it
is identical to !atomic_read(&page->xpfo_mapcount).
next prev parent reply other threads:[~2019-04-04 7:43 UTC|newest]
Thread overview: 102+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-03 17:34 [RFC PATCH v9 00/13] Add support for eXclusive Page Frame Ownership Khalid Aziz
2019-04-03 17:34 ` [RFC PATCH v9 11/13] xpfo, mm: optimize spinlock usage in xpfo_kunmap Khalid Aziz
[not found] ` <5bab13e12d4215112ad2180106cc6bb9b513754a.1554248002.git.khalid.aziz-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
2019-04-04 7:56 ` Peter Zijlstra
2019-04-04 16:06 ` Khalid Aziz
[not found] ` <cover.1554248001.git.khalid.aziz-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
2019-04-03 17:34 ` [RFC PATCH v9 01/13] mm: add MAP_HUGETLB support to vm_mmap Khalid Aziz
2019-04-03 17:34 ` [RFC PATCH v9 02/13] x86: always set IF before oopsing from page fault Khalid Aziz
[not found] ` <e6c57f675e5b53d4de266412aa526b7660c47918.1554248002.git.khalid.aziz-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
2019-04-04 0:12 ` Andy Lutomirski
[not found] ` <CALCETrXvwuwkVSJ+S5s7wTBkNNj3fRVxpx9BvsXWrT=3ZdRnCw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-04-04 1:42 ` Tycho Andersen
2019-04-04 4:12 ` Andy Lutomirski
[not found] ` <CALCETrVp37Xo3EMHkeedP1zxUMf9og=mceBa8c55e1F4G1DRSQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-04-04 15:47 ` Tycho Andersen
2019-04-04 16:23 ` Sebastian Andrzej Siewior
2019-04-04 16:28 ` Thomas Gleixner
[not found] ` <alpine.DEB.2.21.1904041822320.1802-ecDvlHI5BZPZikZi3RtOZ1XZhhPuCNm+@public.gmane.org>
2019-04-04 17:11 ` Andy Lutomirski
2019-04-03 17:34 ` [RFC PATCH v9 03/13] mm: Add support for eXclusive Page Frame Ownership (XPFO) Khalid Aziz
[not found] ` <f1ac3700970365fb979533294774af0b0dd84b3b.1554248002.git.khalid.aziz-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
2019-04-04 7:21 ` Peter Zijlstra
[not found] ` <20190404072152.GN4038-Nxj+rRp3nVydTX5a5knrm8zTDFooKrT+cvkQGrU6aU0@public.gmane.org>
2019-04-04 9:25 ` Peter Zijlstra
2019-04-04 14:48 ` Tycho Andersen
2019-04-04 7:43 ` Peter Zijlstra [this message]
[not found] ` <20190404074323.GO4038-Nxj+rRp3nVydTX5a5knrm8zTDFooKrT+cvkQGrU6aU0@public.gmane.org>
2019-04-04 15:15 ` Khalid Aziz
[not found] ` <b414bacc-2883-1914-38ec-3d8f4a032e10-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
2019-04-04 17:01 ` Peter Zijlstra
2019-04-17 16:15 ` Ingo Molnar
2019-04-17 16:15 ` Ingo Molnar
[not found] ` <20190417161042.GA43453-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2019-04-17 16:49 ` Khalid Aziz
2019-04-17 16:49 ` Khalid Aziz
2019-04-17 17:09 ` Ingo Molnar
2019-04-17 17:09 ` Ingo Molnar
2019-04-17 17:19 ` Nadav Amit
2019-04-17 17:19 ` Nadav Amit
2019-04-17 17:26 ` Ingo Molnar
2019-04-17 17:26 ` Ingo Molnar
2019-04-17 17:44 ` Nadav Amit
2019-04-17 17:44 ` Nadav Amit
2019-04-17 21:19 ` Thomas Gleixner
2019-04-17 21:19 ` Thomas Gleixner
[not found] ` <alpine.DEB.2.21.1904172317460.3174-ecDvlHI5BZPZikZi3RtOZ1XZhhPuCNm+@public.gmane.org>
2019-04-17 23:18 ` Linus Torvalds
2019-04-17 23:18 ` Linus Torvalds
2019-04-17 23:42 ` Thomas Gleixner
2019-04-17 23:42 ` Thomas Gleixner
2019-04-17 23:52 ` Linus Torvalds
2019-04-17 23:52 ` Linus Torvalds
2019-04-18 4:41 ` Andy Lutomirski
2019-04-18 4:41 ` Andy Lutomirski
2019-04-18 5:41 ` Kees Cook
2019-04-18 5:41 ` Kees Cook via iommu
2019-04-18 14:34 ` Khalid Aziz
2019-04-18 14:34 ` Khalid Aziz
2019-04-22 19:30 ` Khalid Aziz
2019-04-22 19:30 ` Khalid Aziz
[not found] ` <8f9d059d-e720-cd24-faa6-45493fc012e0-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
2019-04-22 22:23 ` Kees Cook via iommu
2019-04-22 22:23 ` Kees Cook via iommu
[not found] ` <CAHk-=whUwOjFW6RjHVM8kNOv1QVLJuHj2Dda0=mpLPdJ1UyatQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-04-18 6:14 ` Thomas Gleixner
2019-04-18 6:14 ` Thomas Gleixner
2019-04-17 17:33 ` Khalid Aziz
2019-04-17 17:33 ` Khalid Aziz
2019-04-17 19:49 ` Andy Lutomirski
2019-04-17 19:49 ` Andy Lutomirski
[not found] ` <CALCETrXFzWFMrV-zDa4QFjB=4WnC9RZmorBko65dLGhymDpeQw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-04-17 19:52 ` Tycho Andersen
2019-04-17 19:52 ` Tycho Andersen
2019-04-17 20:12 ` Khalid Aziz
2019-04-17 20:12 ` Khalid Aziz
2019-05-01 14:49 ` Waiman Long
2019-05-01 14:49 ` Waiman Long
2019-05-01 15:18 ` Khalid Aziz
2019-05-01 15:18 ` Khalid Aziz
2019-04-03 17:34 ` [RFC PATCH v9 04/13] xpfo, x86: Add support for XPFO for x86-64 Khalid Aziz
[not found] ` <c15e7d09dfe3dfdb9947d39ed0ddd6573ff86dbf.1554248002.git.khalid.aziz-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
2019-04-04 7:52 ` Peter Zijlstra
[not found] ` <20190404075206.GP4038-Nxj+rRp3nVydTX5a5knrm8zTDFooKrT+cvkQGrU6aU0@public.gmane.org>
2019-04-04 15:40 ` Khalid Aziz
2019-04-03 17:34 ` [RFC PATCH v9 05/13] mm: add a user_virt_to_phys symbol Khalid Aziz
2019-04-03 17:34 ` [RFC PATCH v9 06/13] lkdtm: Add test for XPFO Khalid Aziz
2019-04-03 17:34 ` [RFC PATCH v9 07/13] arm64/mm: Add support " Khalid Aziz
2019-04-03 17:34 ` [RFC PATCH v9 08/13] swiotlb: Map the buffer if it was unmapped by XPFO Khalid Aziz
2019-04-03 17:34 ` [RFC PATCH v9 09/13] xpfo: add primitives for mapping underlying memory Khalid Aziz
2019-04-03 17:34 ` [RFC PATCH v9 10/13] arm64/mm, xpfo: temporarily map dcache regions Khalid Aziz
2019-04-03 17:34 ` [RFC PATCH v9 12/13] xpfo, mm: Defer TLB flushes for non-current CPUs (x86 only) Khalid Aziz
[not found] ` <4495dda4bfc4a06b3312cc4063915b306ecfaecb.1554248002.git.khalid.aziz-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
2019-04-04 4:10 ` Andy Lutomirski
[not found] ` <CALCETrXMXxnWqN94d83UvGWhkD1BNWiwvH2vsUth1w0T3=0ywQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-04-04 22:55 ` Khalid Aziz
[not found] ` <91f1dbce-332e-25d1-15f6-0e9cfc8b797b-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
2019-04-05 7:17 ` Thomas Gleixner
[not found] ` <alpine.DEB.2.21.1904050909520.1802-ecDvlHI5BZPZikZi3RtOZ1XZhhPuCNm+@public.gmane.org>
2019-04-05 14:44 ` Dave Hansen
[not found] ` <26b00051-b03c-9fce-1446-52f0d6ed52f8-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2019-04-05 15:24 ` Andy Lutomirski
2019-04-05 15:24 ` Andy Lutomirski
[not found] ` <DFA69954-3F0F-4B79-A9B5-893D33D87E51-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>
2019-04-05 15:56 ` Tycho Andersen
2019-04-05 15:56 ` Tycho Andersen
2019-04-05 16:32 ` Andy Lutomirski
2019-04-05 16:32 ` Andy Lutomirski
2019-04-05 15:56 ` Khalid Aziz
2019-04-05 15:56 ` Khalid Aziz
2019-04-05 16:01 ` Dave Hansen
2019-04-05 16:01 ` Dave Hansen
[not found] ` <36b999d4-adf6-08a3-2897-d77b9cba20f8-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2019-04-05 16:27 ` Andy Lutomirski
2019-04-05 16:27 ` Andy Lutomirski
[not found] ` <E0BBD625-6FE0-4A8A-884B-E10FAFC3319E-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>
2019-04-05 16:41 ` Peter Zijlstra
2019-04-05 16:41 ` Peter Zijlstra
2019-04-05 17:35 ` Khalid Aziz
2019-04-05 17:35 ` Khalid Aziz
2019-04-05 15:44 ` Khalid Aziz
2019-04-05 15:44 ` Khalid Aziz
2019-04-05 15:24 ` Andy Lutomirski
2019-04-05 15:24 ` Andy Lutomirski
2019-04-04 8:18 ` Peter Zijlstra
2019-04-03 17:34 ` [RFC PATCH v9 13/13] xpfo, mm: Optimize XPFO TLB flushes by batching them together Khalid Aziz
2019-04-06 6:40 ` [RFC PATCH v9 00/13] Add support for eXclusive Page Frame Ownership Jon Masters
2019-04-06 6:40 ` Jon Masters
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