Messages in this thread |  | | | Date | Thu, 13 Jan 2005 10:16:58 -0800 (PST) | | From | Christoph Lameter <> | | Subject | Re: page table lock patch V15 [0/7]: overview |
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On Thu, 13 Jan 2005, Andi Kleen wrote:
> The rule in i386/x86-64 is that you cannot set the PTE in a non atomic way > when its present bit is set (because the hardware could asynchronously > change bits in the PTE that would get lost). Atomic way means clearing > first and then replacing in an atomic operation.
Hmm. I replaced that portion in the swapper with an xchg operation and inspect the result later. Clearing a pte and then setting it to something would open a window for the page fault handler to set up a new pte there since it does not take the page_table_lock. That xchg must be atomic for PAE mode to work then.
> This helps you because you shouldn't be looking at the pte anyways > when pte_present is false. When it is not false it is always updated > atomically.
so pmd_present, pud_none and pgd_none could be considered atomic even if the pm/u/gd_t is a multi-word entity? In that case the current approach would work for higher level entities and in particular S/390 would be in the clear.
But then the issues of replacing multi-word ptes on i386 PAE remain. If no write lock is held on mmap_sem then all writes to pte's must be atomic in order for the get_pte_atomic operation to work reliably. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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