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From: Ben Sanda <Ben.Sanda@dornerworks.com>
To: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: Julien Grall <julien.grall@arm.com>,
	George Dunlap <george.dunlap@citrix.com>
Subject: Re: [PATCH 3/6] xentrace: P2M lookup suport for ARM platform
Date: Mon, 28 Mar 2016 18:55:34 +0000	[thread overview]
Message-ID: <A2A949C387F3A54C9B4DAC2DCD2E9A85E3337CFF@Quimby.dw.local> (raw)
In-Reply-To: <56EAD987.6080204@arm.com>

Julien and George,

Thank you for the comments. I had one question I wanted to ask.

>A DOMID_XEN page could be read only too. For instance, the meta-data
>of the trace buffer is read-only (see t_info), we don't want a domain
>to be able to overwrite them.

>However, all the foreign page are mapped read-write. You will need to
>rework the code to map a foreign domain (see
>XENMAPSPACE_gmfn_foreign) to allow read-only foreign page (maybe by
>adding a new p2m_type_t?).

I understand what you are saying in general, but I'm not familiar
enough with the Xen memory mapping system to know how to actually
implement this. The p2m_type_t p2m_ram_ro exists, which I could assign
to read-only pages, but I'm unsure as to how to detect whether a
request is to a read only mapping or a read-write. The normal (non
DOMID_XEN) p2m_lookup function normally does this by reading the root-
level page tables and somehow extracting the mapping type from the
lpae_t structure. Given that we are not looking up the page tables for
non-translated addresses, I'm not sure where/how to find the correct
mapping type. Can I still lookup the page table entries for the MFN
address and extract the p2m_type_t the same way?

Thank you for any insight or assistance,
Ben
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  reply	other threads:[~2016-03-28 18:58 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-16 20:51 [PATCH 0/6] xentrace/xenalyze support on ARM Benjamin Sanda
2016-03-16 20:51 ` [PATCH 1/6] Flask: Support for ARM xentrace Benjamin Sanda
2016-03-17 14:56   ` Julien Grall
2016-03-17 15:03   ` Julien Grall
2016-03-25 19:27   ` Konrad Rzeszutek Wilk
2016-03-28 15:52     ` Ben Sanda
2016-03-16 20:51 ` [PATCH 2/6] xenalyze: Support for ARM platform Benjamin Sanda
2016-03-16 20:59   ` Andrew Cooper
2016-03-17 10:39     ` George Dunlap
2016-03-16 20:51 ` [PATCH 3/6] xentrace: P2M lookup suport " Benjamin Sanda
2016-03-17 16:21   ` Julien Grall
2016-03-28 18:55     ` Ben Sanda [this message]
2016-03-30 18:38       ` Julien Grall
2016-03-16 20:51 ` [PATCH 4/6] xentrace: ARM platform DOMID_XEN mapping support Benjamin Sanda
2016-03-17 15:53   ` Julien Grall
2016-03-16 20:51 ` [PATCH 5/6] xentrace: Trace buffer support for ARM platform Benjamin Sanda
2016-03-16 20:51 ` [PATCH 6/6] xentrace: ARM platform timestamp support Benjamin Sanda
2016-03-25 19:31   ` Konrad Rzeszutek Wilk
2016-03-31 16:38     ` Stefano Stabellini
2016-03-31 16:44       ` Ben Sanda
2016-04-01 13:05         ` Stefano Stabellini
2016-03-17 15:00 ` [PATCH 0/6] xentrace/xenalyze support on ARM Julien Grall
2016-03-17 16:50   ` Ben Sanda
2016-03-17 17:01     ` Julien Grall
2016-03-17 17:04       ` Ben Sanda
2016-03-18 17:12         ` Wei Liu
2016-03-17 17:23 ` George Dunlap

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