From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
To: Olaf Hering <olaf@aepfle.de>
Cc: xen-devel@lists.xen.org, david.vrabel@citrix.com,
Jan Beulich <JBeulich@suse.com>
Subject: Re: identify a Xen PV domU to fix devmem_is_allowed
Date: Tue, 22 Mar 2016 14:37:03 -0400 [thread overview]
Message-ID: <56F190CF.8010305@oracle.com> (raw)
In-Reply-To: <56F067D5.1040404@oracle.com>
On 03/21/2016 05:29 PM, Boris Ostrovsky wrote:
> On 03/15/2016 12:57 PM, Olaf Hering wrote:
>> On Tue, Mar 01, Boris Ostrovsky wrote:
>>
>>> on domU:
>>>
>>> [root@dhcp-burlington7-2nd-B-east-10-152-55-140 ~]# od -N 1 -j 4096
>>> /dev/mem
>>> od: /dev/mem: read error: Bad address
>>> 0010000
>>> [root@dhcp-burlington7-2nd-B-east-10-152-55-140 ~]#
>>>
>>> with
>>>
>>> (XEN) mm.c:1767:d14v0 Bad L1 flags 10
>> How should we proceed with this bug?
>>
>
> I can't see any way to avoid calling xen_pv_domain() so what you
> suggested should work. The only problem is that this will now cause
> reserved areas to also return 0:
>
> # head /proc/iomem
> 00000000-00000fff : reserved <====
> 00001000-0009ffff : System RAM
> 000a0000-000fffff : reserved <=====
> 000f0000-000fffff : System ROM
> 00100000-7fffffff : System RAM
> 01000000-0172a065 : Kernel code
> 0172a066-01d32b3f : Kernel data
> 01ec5000-02026fff : Kernel bss
> fee00000-fee00fff : Local APIC
>
> which I don't think they really should.
>
> How about this:
>
> if (pagenr < 256 && !xen_pv_domain())
> return 1;
> if (iomem_is_exclusive(pagenr << PAGE_SHIFT))
> return 0;
> if (!page_is_ram(pagenr))
> return 1;
>
>
> Also, while looking into this I noticed that pat_x_mtrr_type() will
> make us switch from _PAGE_CACHE_MODE_WB to _PAGE_CACHE_MODE_UC_MINUS
> when trying to mmap and this is what causes the hypervisor error
> message and the splat in Linux. We make this switch despite the fact
> that MTRR is disabled and therefore mtrr_type_lookup() returns
> MTRR_TYPE_INVALID.
>
> Should we return req_type is MTRR is disabled?
Olaf,
Can you apply PAT changes from
http://lists.xenproject.org/archives/html/xen-devel/2016-03/msg02127.html and
see if it helps?
It should at least get rid of the splat (patch 3 is the one addresses
no-MTRR problem that I mentioned above). We should still fix
devmem_is_allowed() though.
-boris
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next prev parent reply other threads:[~2016-03-22 18:37 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-29 10:28 identify a Xen PV domU to fix devmem_is_allowed Olaf Hering
2016-02-29 15:10 ` Konrad Rzeszutek Wilk
2016-02-29 15:29 ` Olaf Hering
2016-02-29 18:32 ` Boris Ostrovsky
2016-03-01 15:14 ` Olaf Hering
2016-03-01 10:38 ` Jan Beulich
2016-03-01 14:34 ` Konrad Rzeszutek Wilk
2016-03-01 14:45 ` Boris Ostrovsky
2016-03-15 16:57 ` Olaf Hering
2016-03-15 18:56 ` Boris Ostrovsky
2016-03-21 21:29 ` Boris Ostrovsky
2016-03-22 18:37 ` Boris Ostrovsky [this message]
2016-03-23 8:28 ` Olaf Hering
2016-06-06 21:17 ` Olaf Hering
2016-03-01 16:23 ` Olaf Hering
2016-03-01 15:29 ` David Vrabel
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