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From: "Andy Lutomirski" <luto@kernel.org>
To: "Dave Hansen" <dave.hansen@intel.com>,
	"Mike Rapoport" <rppt@kernel.org>,
	linux-mm@kvack.org
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
	"Dave Hansen" <dave.hansen@linux.intel.com>,
	"Ira Weiny" <ira.weiny@intel.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Mike Rapoport" <rppt@linux.ibm.com>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	"Rick P Edgecombe" <rick.p.edgecombe@intel.com>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 4/4] x86/mm: write protect (most) page tables
Date: Mon, 23 Aug 2021 20:34:05 -0700	[thread overview]
Message-ID: <8b50991d-2ab5-4577-83e9-a2d74135c5f5@www.fastmail.com> (raw)
In-Reply-To: <1cccc2b6-8b5b-4aee-483d-f10e64a248a5@intel.com>



On Mon, Aug 23, 2021, at 4:50 PM, Dave Hansen wrote:
> On 8/23/21 6:25 AM, Mike Rapoport wrote:
> >  void ___pte_free_tlb(struct mmu_gather *tlb, struct page *pte)
> >  {
> > +	enable_pgtable_write(page_address(pte));
> >  	pgtable_pte_page_dtor(pte);
> >  	paravirt_release_pte(page_to_pfn(pte));
> >  	paravirt_tlb_remove_table(tlb, pte);
> > @@ -69,6 +73,7 @@ void ___pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd)
> >  #ifdef CONFIG_X86_PAE
> >  	tlb->need_flush_all = 1;
> >  #endif
> > +	enable_pgtable_write(pmd);
> >  	pgtable_pmd_page_dtor(page);
> >  	paravirt_tlb_remove_table(tlb, page);
> >  }
> 
> I would expected this to have leveraged the pte_offset_map/unmap() code
> to enable/disable write access.  Granted, it would enable write access
> even when only a read is needed, but that could be trivially fixed with
> having a variant like:
> 
> 	pte_offset_map_write()
> 	pte_offset_unmap_write()

I would also like to see a discussion of how races in which multiple threads or CPUs access ptes in the same page at the same time.

> 
> in addition to the existing (presumably read-only) versions:
> 
> 	pte_offset_map()
> 	pte_offset_unmap()
> 
> Although those only work for the leaf levels, it seems a shame not to to
> use them.
> 
> I'm also cringing a bit at hacking this into the page allocator.   A
> *lot* of what you're trying to do with getting large allocations out and
> splitting them up is done very well today by the slab allocators.  It
> might take some rearrangement of 'struct page' metadata to be more slab
> friendly, but it does seem like a close enough fit to warrant investigating.
> 

  reply	other threads:[~2021-08-24  3:34 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-23 13:25 [RFC PATCH 0/4] mm/page_alloc: cache pte-mapped allocations Mike Rapoport
2021-08-23 13:25 ` [RFC PATCH 1/4] list: Support getting most recent element in list_lru Mike Rapoport
2021-08-23 13:25 ` [RFC PATCH 2/4] list: Support list head not in object for list_lru Mike Rapoport
2021-08-23 13:25 ` [RFC PATCH 3/4] mm/page_alloc: introduce __GFP_PTE_MAPPED flag to allocate pte-mapped pages Mike Rapoport
2021-08-23 20:29   ` Edgecombe, Rick P
2021-08-24 13:02     ` Mike Rapoport
2021-08-24 16:38       ` Edgecombe, Rick P
2021-08-24 16:54         ` Mike Rapoport
2021-08-24 17:23           ` Edgecombe, Rick P
2021-08-24 17:37             ` Mike Rapoport
2021-08-24 16:12   ` Vlastimil Babka
2021-08-25  8:43   ` David Hildenbrand
2021-08-23 13:25 ` [RFC PATCH 4/4] x86/mm: write protect (most) page tables Mike Rapoport
2021-08-23 20:08   ` Edgecombe, Rick P
2021-08-23 23:50   ` Dave Hansen
2021-08-24  3:34     ` Andy Lutomirski [this message]
2021-08-25 14:59       ` Dave Hansen
2021-08-24 13:32     ` Mike Rapoport
2021-08-25  8:38     ` David Hildenbrand
2021-08-26  8:02     ` Mike Rapoport
2021-08-26  9:01       ` Vlastimil Babka
     [not found]   ` <FB6C09CD-9CEA-4FE8-B179-98DB63EBDD68@gmail.com>
2021-08-24  5:34     ` Nadav Amit
2021-08-24 13:36       ` Mike Rapoport
2021-08-23 20:02 ` [RFC PATCH 0/4] mm/page_alloc: cache pte-mapped allocations Edgecombe, Rick P
2021-08-24 13:03   ` Mike Rapoport
2021-08-24 16:09 ` Vlastimil Babka
2021-08-29  7:06   ` Mike Rapoport

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