linux-kernel - Re: [PATCH 1/1] arm64/hugetlb: clear PG_dcache

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Date:	Thu, 7 Jul 2016 16:37:42 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Zhen Lei <thunder.leizhen@...wei.com>
Cc:	Will Deacon <will.deacon@....com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Xinwei Hu <huxinwei@...wei.com>, Zefan Li <lizefan@...wei.com>,
	Hanjun Guo <guohanjun@...wei.com>,
	Tianhong Ding <dingtianhong@...wei.com>,
	Steve Capper <Steve.Capper@....com>,
	David Woods <dwoods@...hip.com>
Subject: Re: [PATCH 1/1] arm64/hugetlb: clear PG_dcache_clean if the page is
 dirty when munmap

On Thu, Jul 07, 2016 at 08:09:04PM +0800, Zhen Lei wrote:
> At present, PG_dcache_clean is only cleared when the related huge page
> is about to be freed. But sometimes, there maybe a process is in charge
> to copy binary codes into a shared memory, and notifies other processes
> to execute base on that. For the first time, there is no problem, because
> the default value of page->flags is PG_dcache_clean cleared. So the cache
> will be maintained at the time of set_pte_at for other processes. But if
> the content of the shared memory have been updated again, there is no
> cache operations, because the PG_dcache_clean is still set.
> 
> For example:
> Process A
> 	open a hugetlbfs file
> 	mmap it as a shared memory
> 	copy some binary codes into it
> 	munmap
> 
> Process B
> 	open the hugetlbfs file
> 	mmap it as a shared memory, executable
> 	invoke the functions in the shared memory
> 	munmap
> 
> repeat the above steps.

Does this work as you would expect with small pages (and for example
shared file mmap)? I don't want to have a different behaviour between
small and huge pages.

-- 
Catalin