From mboxrd@z Thu Jan  1 00:00:00 1970
From: catalin.marinas@arm.com (Catalin Marinas)
Date: Wed, 20 Jul 2016 10:19:39 +0100
Subject: [PATCH 1/1] arm64/hugetlb: clear PG_dcache_clean if the page is
 dirty when munmap
In-Reply-To: <578EE603.9020206@huawei.com>
References: <1467893344-8352-1-git-send-email-thunder.leizhen@huawei.com>
 <20160707153741.GC27180@e104818-lin.cambridge.arm.com>
 <577F1FD9.1040205@huawei.com>
 <20160708135447.GB22099@e104818-lin.cambridge.arm.com>
 <577FC5AA.5010709@huawei.com>
 <20160708161347.GC22099@e104818-lin.cambridge.arm.com>
 <57839474.6030203@huawei.com>
 <20160712153535.GH22183@e104818-lin.cambridge.arm.com>
 <578EE603.9020206@huawei.com>
Message-ID: <20160720091939.GA25890@e104818-lin.cambridge.arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Wed, Jul 20, 2016 at 10:46:27AM +0800, Leizhen (ThunderTown) wrote:
> >>>> On 2016/7/8 21:54, Catalin Marinas wrote:
> >>>>> ------------8<----------------
> >>>>> diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
> >>>>> index dbd12ea8ce68..c753fa804165 100644
> >>>>> --- a/arch/arm64/mm/flush.c
> >>>>> +++ b/arch/arm64/mm/flush.c
> >>>>> @@ -75,7 +75,8 @@ void __sync_icache_dcache(pte_t pte, unsigned long addr)
> >>>>>  	if (!page_mapping(page))
> >>>>>  		return;
> >>>>>  
> >>>>> -	if (!test_and_set_bit(PG_dcache_clean, &page->flags))
> >>>>> +	if (!test_and_set_bit(PG_dcache_clean, &page->flags) ||
> >>>>> +	    PageDirty(page))
> >>>>>  		sync_icache_aliases(page_address(page),
> >>>>>  				    PAGE_SIZE << compound_order(page));
> >>>>>  	else if (icache_is_aivivt())
> >>>>> ----------------8<---------------------
> 
> Do you plan to send this patch? My colleagues told me that if our
> patches are quite different, it should be Signed-off-by you.

The reason I'm not sending it is that I don't fully understand how it
solves the problem for a shared file mmap(), not just hugetlbfs. As I
said in an earlier email: after an msync() in user space we
should flush the pages to disk via write_cache_pages(). This function
calls clear_page_dirty_for_io() after which PageDirty() is no longer
true. I can't tell how a subsequent mmap() can see the written pages as
dirty.

> I searched all Linux source code, __sync_icache_dcache is only called
> by set_pte_at, and some check conditions(especially pte_exec) will
> limit its impact.
> 
> 	if (pte_user(pte) && pte_exec(pte) && !pte_special(pte))
> 		__sync_icache_dcache(pte, addr);

Yes, and set_pte_at() would be called as a result of a page fault when
accessing the mmap'ed file.

-- 
Catalin