From: julien.grall@linaro.org (Julien Grall) To: linux-arm-kernel@lists.infradead.org Subject: [Xen-devel] [RFC PATCH 0/2] xen/arm: fix "xen_add_mach_to_phys_entry: cannot add" problem Date: Tue, 08 Jul 2014 10:37:35 +0100 [thread overview] Message-ID: <53BBBBDF.4090309@linaro.org> (raw) In-Reply-To: <alpine.DEB.2.02.1407072007470.27641@kaball.uk.xensource.com> On 07/07/14 21:24, Stefano Stabellini wrote: > Hi all, Hi Stefano, > Xen support in Linux for ARM and ARM64 suffers from lack of support for > multiple mfn to pfn mappings: whenever a frontend grants the same page > multiple times to the backend, the mfn to pfn accounting in > arch/arm/xen/p2m.c fails. The issue has become critical since v3.15, > when xen-netfront/xen-netback switched from grant copies to grant > mappings, therefore causing the issue to happen much more often. > > Fixing the mfn to pfn accounting in p2m.c is difficult and expensive, > therefore we are looking for alternative solutions. One idea is avoiding > mfn to pfn conversions altogether. The only code path that needs them is > swiotlb-xen:unmap_page (and single_for_cpu and single_for_device). > > To avoid mfn to pfn conversions we rely on a second p2m mapping done by > Xen, see the attached patch. In Linux we use it to perform the cache > maintenance operations without mfns conversions. I tried this series on midway with a FreeBSD guest. I got those errors in DOM0 log: xen_add_phys_to_mach_entry: cannot add pfn=0x002d99330003cdc7 -> mfn=0x00000001002d9933: pfn=0x002d99330003e3ea -> mfn=0x00000001002d9933 already exists xen_add_phys_to_mach_entry: cannot add pfn=0x002d99330003d47a -> mfn=0x00000001002d9933: pfn=0x002d99330003e3ea -> mfn=0x00000001002d9933 already exists It looks like you forgot to modify xen_add_phys_to_mach_entry. Regards, -- Julien Grall
WARNING: multiple messages have this Message-ID (diff)
From: Julien Grall <julien.grall@linaro.org> To: Stefano Stabellini <stefano.stabellini@eu.citrix.com>, xen-devel@lists.xensource.com Cc: Julien Grall <julien.grall@citrix.com>, v1ne2go@gmail.com, Ian Campbell <Ian.Campbell@citrix.com>, linux-arm-kernel@lists.infradead.org, David Vrabel <david.vrabel@citrix.com> Subject: Re: [Xen-devel] [RFC PATCH 0/2] xen/arm: fix "xen_add_mach_to_phys_entry: cannot add" problem Date: Tue, 08 Jul 2014 10:37:35 +0100 [thread overview] Message-ID: <53BBBBDF.4090309@linaro.org> (raw) In-Reply-To: <alpine.DEB.2.02.1407072007470.27641@kaball.uk.xensource.com> On 07/07/14 21:24, Stefano Stabellini wrote: > Hi all, Hi Stefano, > Xen support in Linux for ARM and ARM64 suffers from lack of support for > multiple mfn to pfn mappings: whenever a frontend grants the same page > multiple times to the backend, the mfn to pfn accounting in > arch/arm/xen/p2m.c fails. The issue has become critical since v3.15, > when xen-netfront/xen-netback switched from grant copies to grant > mappings, therefore causing the issue to happen much more often. > > Fixing the mfn to pfn accounting in p2m.c is difficult and expensive, > therefore we are looking for alternative solutions. One idea is avoiding > mfn to pfn conversions altogether. The only code path that needs them is > swiotlb-xen:unmap_page (and single_for_cpu and single_for_device). > > To avoid mfn to pfn conversions we rely on a second p2m mapping done by > Xen, see the attached patch. In Linux we use it to perform the cache > maintenance operations without mfns conversions. I tried this series on midway with a FreeBSD guest. I got those errors in DOM0 log: xen_add_phys_to_mach_entry: cannot add pfn=0x002d99330003cdc7 -> mfn=0x00000001002d9933: pfn=0x002d99330003e3ea -> mfn=0x00000001002d9933 already exists xen_add_phys_to_mach_entry: cannot add pfn=0x002d99330003d47a -> mfn=0x00000001002d9933: pfn=0x002d99330003e3ea -> mfn=0x00000001002d9933 already exists It looks like you forgot to modify xen_add_phys_to_mach_entry. Regards, -- Julien Grall
next prev parent reply other threads:[~2014-07-08 9:37 UTC|newest] Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top 2014-07-07 20:24 [RFC PATCH 0/2] xen/arm: fix "xen_add_mach_to_phys_entry: cannot add" problem Stefano Stabellini 2014-07-07 20:24 ` Stefano Stabellini 2014-07-07 20:26 ` [RFC PATCH 1/2] xen/arm: reimplement xen_dma_unmap_page & friends Stefano Stabellini 2014-07-07 20:26 ` Stefano Stabellini 2014-07-07 20:26 ` [RFC PATCH 2/2] xen/arm: remove mach_to_phys rbtree Stefano Stabellini 2014-07-07 20:26 ` Stefano Stabellini 2014-07-08 8:32 ` [RFC PATCH 0/2] xen/arm: fix "xen_add_mach_to_phys_entry: cannot add" problem Julien Grall 2014-07-08 9:37 ` Julien Grall [this message] 2014-07-08 9:37 ` [Xen-devel] " Julien Grall 2014-07-08 10:50 ` David Vrabel 2014-07-08 10:50 ` David Vrabel 2014-07-08 11:00 ` Stefano Stabellini 2014-07-08 11:00 ` Stefano Stabellini 2014-07-08 11:06 ` Ian Campbell 2014-07-08 11:06 ` Ian Campbell
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