From: Dave Hansen <dave.hansen@intel.com>
To: Andy Lutomirski <luto@kernel.org>,
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: Wed, 25 Aug 2021 07:59:49 -0700 [thread overview]
Message-ID: <a24105be-b07f-41e5-4c3e-0b8a911ce231@intel.com> (raw)
In-Reply-To: <8b50991d-2ab5-4577-83e9-a2d74135c5f5@www.fastmail.com>
On 8/23/21 8:34 PM, Andy Lutomirski wrote:
>> 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.
Yeah, the 32-bit highmem code has a per-cpu mapping area for
kmap_atomic() that lies underneath the pte_offset_map(). Although it's
in the shared kernel mapping, only one CPU uses it.
I didn't look at it until you mentioned it, but the code in this set is
just plain buggy if two CPUs do a
enable_pgtable_write()/disable_pgtable_write(). They'll clobber each other:
> +static void pgtable_write_set(void *pg_table, bool set)
> +{
> + int level = 0;
> + pte_t *pte;
> +
> + /*
> + * Skip the page tables allocated from pgt_buf break area and from
> + * memblock
> + */
> + if (!after_bootmem)
> + return;
> + if (!PageTable(virt_to_page(pg_table)))
> + return;
> +
> + pte = lookup_address((unsigned long)pg_table, &level);
> + if (!pte || level != PG_LEVEL_4K)
> + return;
> +
> + if (set) {
> + if (pte_write(*pte))
> + return;
> +
> + WRITE_ONCE(*pte, pte_mkwrite(*pte));
> + } else {
> + if (!pte_write(*pte))
> + return;
> +
> + WRITE_ONCE(*pte, pte_wrprotect(*pte));
> + }
> +}
next prev parent reply other threads:[~2021-08-25 14:59 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
2021-08-25 14:59 ` Dave Hansen [this message]
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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