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From: David Vrabel <david.vrabel@citrix.com>
To: Daniel Kiper <daniel.kiper@oracle.com>,
	crash-utility@redhat.com, kexec@lists.infradead.org,
	linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org
Cc: jgross@suse.com, olaf@aepfle.de, keir@xen.org, dmair@suse.com,
	andrew.cooper3@citrix.com, ptesarik@suse.cz, dslutz@verizon.com,
	anderson@redhat.com, david.vrabel@citrix.com, jbeulich@suse.com,
	boris.ostrovsky@oracle.com
Subject: Re: [Xen-devel] [PATCH] xen: Add support for dom0 with Linux kernel 3.19 and newer
Date: Fri, 22 Jan 2016 10:03:34 +0000	[thread overview]
Message-ID: <56A1FE76.40201@citrix.com> (raw)
In-Reply-To: <1453407231-25432-1-git-send-email-daniel.kiper@oracle.com>

On 21/01/16 20:13, Daniel Kiper wrote:
> Linux kernel commit 054954eb051f35e74b75a566a96fe756015352c8
> (xen: switch to linear virtual mapped sparse p2m list), which
> appeared in 3.19, introduced linear virtual mapped sparse p2m
> list. If readmem() reads p2m then it access this list using
> physical addresses. Sadly, VMA to physical address translation
> in crash requires access to p2m list. This means that we have
> a chicken and egg problem. In general this issue must be solved
> by introducing some changes in libxl, Linux kernel and crash
> (I have added this task to my long TODO list). However, in dom0
> case we can use crash_xen_info_t.dom0_pfn_to_mfn_frame_list_list
> which is available out of the box. So, let's use it and make
> at least some users happy.

I'm confused.  How does a virtual address to (pseudo-)physical address
lookup require access to the p2m?  Surely this is a walk of the page
tables followed by a M2P lookup on the MFN in the L1 PTE?

David

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WARNING: multiple messages have this Message-ID (diff)
From: David Vrabel <david.vrabel@citrix.com>
To: Daniel Kiper <daniel.kiper@oracle.com>,
	<crash-utility@redhat.com>, <kexec@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>, <xen-devel@lists.xenproject.org>
Cc: <jgross@suse.com>, <olaf@aepfle.de>, <keir@xen.org>,
	<jbeulich@suse.com>, <andrew.cooper3@citrix.com>,
	<ptesarik@suse.cz>, <dslutz@verizon.com>, <anderson@redhat.com>,
	<david.vrabel@citrix.com>, <dmair@suse.com>,
	<boris.ostrovsky@oracle.com>
Subject: Re: [Xen-devel] [PATCH] xen: Add support for dom0 with Linux kernel 3.19 and newer
Date: Fri, 22 Jan 2016 10:03:34 +0000	[thread overview]
Message-ID: <56A1FE76.40201@citrix.com> (raw)
In-Reply-To: <1453407231-25432-1-git-send-email-daniel.kiper@oracle.com>

On 21/01/16 20:13, Daniel Kiper wrote:
> Linux kernel commit 054954eb051f35e74b75a566a96fe756015352c8
> (xen: switch to linear virtual mapped sparse p2m list), which
> appeared in 3.19, introduced linear virtual mapped sparse p2m
> list. If readmem() reads p2m then it access this list using
> physical addresses. Sadly, VMA to physical address translation
> in crash requires access to p2m list. This means that we have
> a chicken and egg problem. In general this issue must be solved
> by introducing some changes in libxl, Linux kernel and crash
> (I have added this task to my long TODO list). However, in dom0
> case we can use crash_xen_info_t.dom0_pfn_to_mfn_frame_list_list
> which is available out of the box. So, let's use it and make
> at least some users happy.

I'm confused.  How does a virtual address to (pseudo-)physical address
lookup require access to the p2m?  Surely this is a walk of the page
tables followed by a M2P lookup on the MFN in the L1 PTE?

David

  parent reply	other threads:[~2016-01-22 10:04 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-21 20:13 [PATCH] xen: Add support for dom0 with Linux kernel 3.19 and newer Daniel Kiper
2016-01-21 20:13 ` Daniel Kiper
2016-01-22 10:03 ` David Vrabel
2016-01-22 10:03 ` David Vrabel [this message]
2016-01-22 10:03   ` [Xen-devel] " David Vrabel
2016-01-22 14:22   ` Daniel Kiper
2016-01-22 14:22     ` Daniel Kiper
2016-01-22 14:22   ` Daniel Kiper

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