Re: [PATCH v9 0/10] iommu/vt-d: Fix intel vt-d faults in kdump kernel
On 04/07/15 at 05:55pm, Li, ZhenHua wrote: > On 04/07/2015 05:08 PM, Dave Young wrote: > >On 04/07/15 at 11:46am, Dave Young wrote: > >>On 04/05/15 at 09:54am, Baoquan He wrote: > >>>On 04/03/15 at 05:21pm, Dave Young wrote: > On 04/03/15 at 05:01pm, Li, ZhenHua wrote: > >Hi Dave, > > > >There may be some possibilities that the old iommu data is corrupted by > >some other modules. Currently we do not have a better solution for the > >dmar faults. > > > >But I think when this happens, we need to fix the module that corrupted > >the old iommu data. I once met a similar problem in normal kernel, the > >queue used by the qi_* functions was written again by another module. > >The fix was in that module, not in iommu module. > > It is too late, there will be no chance to save vmcore then. > > Also if it is possible to continue corrupt other area of oldmem because > of using old iommu tables then it will cause more problems. > > So I think the tables at least need some verifycation before being used. > > >>> > >>>Yes, it's a good thinking anout this and verification is also an > >>>interesting idea. kexec/kdump do a sha256 calculation on loaded kernel > >>>and then verify this again when panic happens in purgatory. This checks > >>>whether any code stomps into region reserved for kexec/kernel and corrupt > >>>the loaded kernel. > >>> > >>>If this is decided to do it should be an enhancement to current > >>>patchset but not a approach change. Since this patchset is going very > >>>close to point as maintainers expected maybe this can be merged firstly, > >>>then think about enhancement. After all without this patchset vt-d often > >>>raised error message, hung. > >> > >>It does not convince me, we should do it right at the beginning instead of > >>introduce something wrong. > >> > >>I wonder why the old dma can not be remap to a specific page in kdump kernel > >>so that it will not corrupt more memory. But I may missed something, I will > >>looking for old threads and catch up. > > > >I have read the old discussion, above way was dropped because it could > >corrupt > >filesystem. Apologize about late commenting. > > > >But current solution sounds bad to me because of using old memory which is > >not > >reliable. > > > >Thanks > >Dave > > > Seems we do not have a better solution for the dmar faults. But I believe > we can find out how to verify the iommu data which is located in old memory. That will be great, thanks. So there's two things: 1) make sure old pg tables are right, this is what we were talking about. 2) avoid writing old memory, I suppose only dma read could corrupt filesystem, right? So how about for any dma writes just create a scratch page in 2nd kernel memory. Only using old page table for dma read. Thanks Dave ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH v9 0/10] iommu/vt-d: Fix intel vt-d faults in kdump kernel
On 04/06/2015 11:46 PM, Dave Young wrote: On 04/05/15 at 09:54am, Baoquan He wrote: On 04/03/15 at 05:21pm, Dave Young wrote: On 04/03/15 at 05:01pm, Li, ZhenHua wrote: Hi Dave, There may be some possibilities that the old iommu data is corrupted by some other modules. Currently we do not have a better solution for the dmar faults. But I think when this happens, we need to fix the module that corrupted the old iommu data. I once met a similar problem in normal kernel, the queue used by the qi_* functions was written again by another module. The fix was in that module, not in iommu module. It is too late, there will be no chance to save vmcore then. Also if it is possible to continue corrupt other area of oldmem because of using old iommu tables then it will cause more problems. So I think the tables at least need some verifycation before being used. Yes, it's a good thinking anout this and verification is also an interesting idea. kexec/kdump do a sha256 calculation on loaded kernel and then verify this again when panic happens in purgatory. This checks whether any code stomps into region reserved for kexec/kernel and corrupt the loaded kernel. If this is decided to do it should be an enhancement to current patchset but not a approach change. Since this patchset is going very close to point as maintainers expected maybe this can be merged firstly, then think about enhancement. After all without this patchset vt-d often raised error message, hung. It does not convince me, we should do it right at the beginning instead of introduce something wrong. I wonder why the old dma can not be remap to a specific page in kdump kernel so that it will not corrupt more memory. But I may missed something, I will looking for old threads and catch up. Thanks Dave The (only) issue is not corruption, but once the iommu is re-configured, the old, not-stopped-yet, dma engines will use iova's that will generate dmar faults, which will be enabled when the iommu is re-configured (even to a single/simple paging scheme) in the kexec kernel. ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH v9 0/10] iommu/vt-d: Fix intel vt-d faults in kdump kernel
On 04/07/2015 05:08 PM, Dave Young wrote: On 04/07/15 at 11:46am, Dave Young wrote: On 04/05/15 at 09:54am, Baoquan He wrote: On 04/03/15 at 05:21pm, Dave Young wrote: On 04/03/15 at 05:01pm, Li, ZhenHua wrote: Hi Dave, There may be some possibilities that the old iommu data is corrupted by some other modules. Currently we do not have a better solution for the dmar faults. But I think when this happens, we need to fix the module that corrupted the old iommu data. I once met a similar problem in normal kernel, the queue used by the qi_* functions was written again by another module. The fix was in that module, not in iommu module. It is too late, there will be no chance to save vmcore then. Also if it is possible to continue corrupt other area of oldmem because of using old iommu tables then it will cause more problems. So I think the tables at least need some verifycation before being used. Yes, it's a good thinking anout this and verification is also an interesting idea. kexec/kdump do a sha256 calculation on loaded kernel and then verify this again when panic happens in purgatory. This checks whether any code stomps into region reserved for kexec/kernel and corrupt the loaded kernel. If this is decided to do it should be an enhancement to current patchset but not a approach change. Since this patchset is going very close to point as maintainers expected maybe this can be merged firstly, then think about enhancement. After all without this patchset vt-d often raised error message, hung. It does not convince me, we should do it right at the beginning instead of introduce something wrong. I wonder why the old dma can not be remap to a specific page in kdump kernel so that it will not corrupt more memory. But I may missed something, I will looking for old threads and catch up. I have read the old discussion, above way was dropped because it could corrupt filesystem. Apologize about late commenting. But current solution sounds bad to me because of using old memory which is not reliable. Thanks Dave Seems we do not have a better solution for the dmar faults. But I believe we can find out how to verify the iommu data which is located in old memory. Thanks Zhenhua ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH v9 0/10] iommu/vt-d: Fix intel vt-d faults in kdump kernel
On 04/07/15 at 11:46am, Dave Young wrote: > On 04/05/15 at 09:54am, Baoquan He wrote: > > On 04/03/15 at 05:21pm, Dave Young wrote: > > > On 04/03/15 at 05:01pm, Li, ZhenHua wrote: > > > > Hi Dave, > > > > > > > > There may be some possibilities that the old iommu data is corrupted by > > > > some other modules. Currently we do not have a better solution for the > > > > dmar faults. > > > > > > > > But I think when this happens, we need to fix the module that corrupted > > > > the old iommu data. I once met a similar problem in normal kernel, the > > > > queue used by the qi_* functions was written again by another module. > > > > The fix was in that module, not in iommu module. > > > > > > It is too late, there will be no chance to save vmcore then. > > > > > > Also if it is possible to continue corrupt other area of oldmem because > > > of using old iommu tables then it will cause more problems. > > > > > > So I think the tables at least need some verifycation before being used. > > > > > > > Yes, it's a good thinking anout this and verification is also an > > interesting idea. kexec/kdump do a sha256 calculation on loaded kernel > > and then verify this again when panic happens in purgatory. This checks > > whether any code stomps into region reserved for kexec/kernel and corrupt > > the loaded kernel. > > > > If this is decided to do it should be an enhancement to current > > patchset but not a approach change. Since this patchset is going very > > close to point as maintainers expected maybe this can be merged firstly, > > then think about enhancement. After all without this patchset vt-d often > > raised error message, hung. > > It does not convince me, we should do it right at the beginning instead of > introduce something wrong. > > I wonder why the old dma can not be remap to a specific page in kdump kernel > so that it will not corrupt more memory. But I may missed something, I will > looking for old threads and catch up. I have read the old discussion, above way was dropped because it could corrupt filesystem. Apologize about late commenting. But current solution sounds bad to me because of using old memory which is not reliable. Thanks Dave ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
