From: Julien Grall <julien.grall@arm.com>
To: George Dunlap <George.Dunlap@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
sstabellini@kernel.org
Cc: Wei Liu <wei.liu2@citrix.com>,
Benjamin Sanda <ben.sanda@dornerworks.com>,
Tim Deegan <tim@xen.org>, Ian Jackson <ian.jackson@eu.citrix.com>,
Jan Beulich <JBeulich@suse.com>,
xen-devel <xen-devel@lists.xenproject.org>,
Keir Fraser <keir@xen.org>
Subject: Re: [PATCH v3 2/5] xentrace: Memory/Page Mapping support for DOMID_XEN on ARM
Date: Tue, 12 Apr 2016 16:53:53 +0100 [thread overview]
Message-ID: <570D1A11.20001@arm.com> (raw)
In-Reply-To: <CAFLBxZZw=Fquz+HsZn_ru3Vb+3-bMNT4LY9JBwM6XDW=Q3XY7g@mail.gmail.com>
Hi George,
On 11/04/2016 10:52, George Dunlap wrote:
> On Fri, Apr 8, 2016 at 6:58 PM, Andrew Cooper <andrew.cooper3@citrix.com> wrote:
>> On 08/04/16 16:49, Jan Beulich wrote:
>>>>>> On 08.04.16 at 12:42, <julien.grall@arm.com> wrote:
>>>> On 04/04/16 19:48, Benjamin Sanda wrote:
>>>>> + else
>>>>> + {
>>>>> + /* retrieve the page to determine read/write or read only mapping */
>>>>> + mfn = paddr >> PAGE_SHIFT;
>>>>> + if (mfn_valid(mfn))
>>>>> + {
>>>>> + page = mfn_to_page(mfn);
>>>>> + *t = (page->u.inuse.type_info == PGT_writable_page ?
>>>>> + p2m_ram_rw : p2m_ram_ro);
>>>> Unfortunately, xenmem_add_to_physmap_one will ignore the return type and
>>>> will always map using the type p2m_map_foreign. I would introduce
>>>> a new type p2m_map_foreign_ro to allow read-only foreign mapping.
>>>>
>>>> I've looked at the x86 code (p2m_add_foreign) and I haven't been able to
>>>> find how the page will be mapped read-only in the guest P2M.
>>>> get_page_from_gfn will always return p2m_raw_rw for DOMID_XEN as it's a
>>>> non translated domain.
>>>>
>>>> Andrew and Jan, do you know how this is supposed to work when xentrace
>>>> is used in a HVM domain? Does x86 Xen always mapped Read-Write the page?
>>> I don't think that case is being taken care of right now: xentrace
>>> is to be used by privileged guests only anyway, and the only
>>> HVM-like privileged guest would be a PVHv1 Dom0 (which likely
>>> no-one cared about to make work with xentrace so far).
>>
>> Answer to questions of the form "Has anyone considered $X for a
>> privileged HVM domain on x86" are almost always "No".
>>
>> The real question is whether the domain making the mapping needs to
>> write into the pages or not. If xentrace has to update shared pointers,
>> then it needs to be rw. If it simply consumes the data without any
>> backwards notification, then it should be ro.
>
> It does access shared pointers, and so needs at lest one page to be
> rw. At the moment there's sort of two levels: the "trace info"
> page(s), mapped RO, which has the list of all the MFNs used for the
> actual trace data, and the trace data MFNs themselves, which are
> mapped RW.
>
> Re Julien's question about how DOMID_XEN pages are marked RO on x86
> when get_page_from_gfn() always returns p2m_ram_rw: The answer is that
> get_page_from_gfn() is only really used by the p2m code. For PV
> guests, it's the page type that restricts a page's type to RO or RW.
> trace.c calls share_xen_page_with_privileged_guests(), which on x86
> calls xen/arch/x86/mm.c:share_xen_page_with_guest(), which sets the
> type to PGT_writable_page.
Thank you for the explanation.
The ARM implementation of share_xen_page_with_guest is nearly the same
as the x86 one. However, the type is never used so far for the P2M code.
So far, all ARM domains have been auto-translated. DOMID_XEN is the
first non auto-translated domain.
We could make DOMID_XEN an auto-translated domain by introducing page
table for dummy domain. This would make the code cleaner but use more
memory (allocation of 3 level of page tables).
Stefano, do you have any opinions on this?
Regards,
--
Julien Grall
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next prev parent reply other threads:[~2016-04-12 15:54 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-04 18:48 [PATCH v3 0/5] xentrace/xenalyze Support on ARM Benjamin Sanda
2016-04-04 18:48 ` [PATCH v3 1/5] xentrace: Common Support for get_pg_owner/put_pg_owner on ARM and x86 Benjamin Sanda
2016-04-04 23:05 ` Andrew Cooper
2016-04-05 8:12 ` Jan Beulich
2016-04-14 19:59 ` Ben Sanda
2016-04-17 7:58 ` Jan Beulich
2016-04-04 18:48 ` [PATCH v3 2/5] xentrace: Memory/Page Mapping support for DOMID_XEN on ARM Benjamin Sanda
2016-04-08 10:42 ` Julien Grall
2016-04-08 15:49 ` Jan Beulich
2016-04-08 17:58 ` Andrew Cooper
2016-04-11 9:52 ` George Dunlap
2016-04-12 15:53 ` Julien Grall [this message]
2016-04-14 19:52 ` Ben Sanda
2016-04-20 12:48 ` Julien Grall
2016-04-22 9:42 ` Stefano Stabellini
2016-04-22 17:01 ` Julien Grall
2016-04-04 18:48 ` [PATCH v3 3/5] xentrace: Timestamp support for ARM platform Benjamin Sanda
2016-04-08 10:50 ` Julien Grall
2016-04-11 14:56 ` Konrad Rzeszutek Wilk
2016-04-04 18:48 ` [PATCH v3 4/5] xentrace: Trace Buffer Initialization on ARM Benjamin Sanda
2016-04-08 10:53 ` Julien Grall
2016-04-04 18:48 ` [PATCH v3 5/5] xenalyze: Build for Both ARM and x86 Platforms Benjamin Sanda
2016-04-05 8:09 ` [PATCH v3 0/5] xentrace/xenalyze Support on ARM Jan Beulich
2016-04-06 16:51 ` Ben Sanda
2016-04-06 16:59 ` Andrew Cooper
2016-04-06 17:03 ` Ben Sanda
2016-04-08 14:44 ` George Dunlap
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