linux-kernel - Re: [PATCH] mm: fix pfn_t to page conversion in vm_insert

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Message-ID: <56A7DBF7.7050204@candw.ms>
Date:	Tue, 26 Jan 2016 16:49:59 -0400
From:	Julian Margetson <runaway@...dw.ms>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Maling list - DRI developers <dri-devel@...ts.freedesktop.org>,
	Dave Hansen <dave@...1.net>, David Airlie <airlied@...ux.ie>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm: fix pfn_t to page conversion in vm_insert_mixed

On 1/26/2016 4:34 PM, Dan Williams wrote:
> On Tue, Jan 26, 2016 at 11:46 AM, Julian Margetson <runaway@...dw.ms> wrote:
>> On 1/26/2016 2:37 PM, Dan Williams wrote:
>>
>> pfn_t_to_page() honors the flags in the pfn_t value to determine if a
>> pfn is backed by a page.  However, vm_insert_mixed() was originally
>> written to use pfn_valid() to make this determination.  To restore the
>> old/correct behavior, ignore the pfn_t flags in the !pfn_t_devmap() case
>> and fallback to trusting pfn_valid().
>>
>> Fixes: 01c8f1c44b83 ("mm, dax, gpu: convert vm_insert_mixed to pfn_t")
>> Cc: Dave Hansen <dave@...1.net>
>> Cc: David Airlie <airlied@...ux.ie>
>> Reported-by: Julian Margetson <runaway@...dw.ms>
>> Reported-by: Tomi Valkeinen <tomi.valkeinen@...com>
>> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
>> ---
>>   mm/memory.c |    9 +++++++--
>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 30991f83d0bf..93ce37989471 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -1591,10 +1591,15 @@ int vm_insert_mixed(struct vm_area_struct *vma,
>> unsigned long addr,
>>    * than insert_pfn).  If a zero_pfn were inserted into a VM_MIXEDMAP
>>    * without pte special, it would there be refcounted as a normal page.
>>    */
>> - if (!HAVE_PTE_SPECIAL && pfn_t_valid(pfn)) {
>> + if (!HAVE_PTE_SPECIAL && !pfn_t_devmap(pfn) && pfn_t_valid(pfn)) {
>>    struct page *page;
>>
>> - page = pfn_t_to_page(pfn);
>> + /*
>> + * At this point we are committed to insert_page()
>> + * regardless of whether the caller specified flags that
>> + * result in pfn_t_has_page() == false.
>> + */
>> + page = pfn_to_page(pfn_t_to_pfn(pfn));
>>    return insert_page(vma, addr, page, vma->vm_page_prot);
>>    }
>>    return insert_pfn(vma, addr, pfn, vma->vm_page_prot);
>>
>>
>>
>> [   16.503323] systemd[1]: Mounting FUSE Control File System...
>> [   42.703092] Oops: Machine check, sig: 7 [#1]
>> [   42.707624] PREEMPT Canyonlands
>> [   42.710959] Modules linked in:
>> [   42.714201] CPU: 0 PID: 553 Comm: Xorg Not tainted 4.5.0-rc1-Sam460ex #1
>> [   42.721283] task: ee1e45c0 ti: ecd46000 task.ti: ecd46000
>> [   42.726983] NIP: 1fed2480 LR: 1fed2404 CTR: 1fed24d0
>> [   42.732227] REGS: ecd47f10 TRAP: 0214   Not tainted  (4.5.0-rc1-Sam460ex)
>> [   42.739395] MSR: 0002d000 <CE,EE,PR,ME>  CR: 28004262  XER: 00000000
>> [   42.746244]
>> GPR00: 1f396134 bfcb0970 b77fc6f0 b6fbeffc b67d5008 00000780 00000004
>> 00000000
>> GPR08: 00000000 b6fbeffc 00000000 bfcb0920 1fed2404 2076dff4 00000000
>> 00000780
>> GPR16: 00000000 00000020 00000000 00000000 00001e00 209be650 00000438
>> b67d5008
>> GPR24: 00000780 bfcb09c8 209a8728 b6fbf000 b6fbf000 b67d5008 1ffdaff4
>> 00001e00
>> [   42.778096] NIP [1fed2480] 0x1fed2480
>> [   42.781967] LR [1fed2404] 0x1fed2404
>> [   42.785741] Call Trace:
>> [   42.943688] ---[ end trace 5d20a91d2d30d9d6 ]---
>> [   42.948311]
>> [   46.641774] Machine check in kernel mode.
>> [   46.645805] Data Write PLB Error
>> [   46.649031] Machine Check exception is imprecise
>> [   46.653658] Vector: 214  at [eccfbf10]
>> [   46.657408]     pc: 1ffa9480
>> [   46.660325]     lr: 1ffa9404
>> [   46.663241]     sp: bf9252b0
>> [   46.666123]    msr: 2d000
>> [   46.668746]   current = 0xee1e73c0
>> [   46.672149]     pid   = 663, comm = Xorg
>> [   46.676074] Linux version 4.5.0-rc1-Sam460ex (root@...ian-VirtualBox)
> Ok, I think the patch is still needed for the issue Tomi reported,
> this appears to be a separate bug.
>
> Can you send me your kernel config?
>
>


View attachment "Sam460ex-4.5-rc1.config" of type "text/plain" (99801 bytes)