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xen-devel
[Xen-devel] Re: [Revert] Re: [PATCH] mm: sync vmalloc address space page
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To: |
David Vrabel <david.vrabel@xxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: [Revert] Re: [PATCH] mm: sync vmalloc address space page tables in alloc_vm_area() |
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From: |
Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> |
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Date: |
Fri, 2 Sep 2011 15:32:04 -0700 |
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Cc: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, "namhyung@xxxxxxxxx" <namhyung@xxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "linux-mm@xxxxxxxxx" <linux-mm@xxxxxxxxx>, "rientjes@xxxxxxxxxx" <rientjes@xxxxxxxxxx>, "paulmck@xxxxxxxxxxxxxxxxxx" <paulmck@xxxxxxxxxxxxxxxxxx> |
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Delivery-date: |
Fri, 02 Sep 2011 15:33:19 -0700 |
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<1314877863-21977-1-git-send-email-david.vrabel@xxxxxxxxxx> <20110901161134.GA8979@xxxxxxxxxxxx> <4E5FED1A.1000300@xxxxxxxx> <20110901141754.76cef93b.akpm@xxxxxxxxxxxxxxxxxxxx> <4E60C067.4010600@xxxxxxxxxx> |
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On Fri, 2 Sep 2011 12:39:19 +0100
David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
> Xen backend drivers (e.g., blkback and netback) would sometimes fail
> to map grant pages into the vmalloc address space allocated with
> alloc_vm_area(). The GNTTABOP_map_grant_ref would fail because Xen
> could not find the page (in the L2 table) containing the PTEs it
> needed to update.
>
> (XEN) mm.c:3846:d0 Could not find L1 PTE for address fbb42000
>
> netback and blkback were making the hypercall from a kernel thread
> where task->active_mm != &init_mm and alloc_vm_area() was only
> updating the page tables for init_mm. The usual method of deferring
> the update to the page tables of other processes (i.e., after taking a
> fault) doesn't work as a fault cannot occur during the hypercall.
>
> This would work on some systems depending on what else was using
> vmalloc.
>
> Fix this by reverting ef691947d8a3d479e67652312783aedcf629320a
> (vmalloc: remove vmalloc_sync_all() from alloc_vm_area()) and add a
> comment to explain why it's needed.
oookay, I queued this for 3.1 and tagged it for a 3.0.x backport. I
*think* that's the outcome of this discussion, for the short-term?
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