[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] an assertion triggered when running Xen on a HSW desktop
On Tue, Jan 15, 2019 at 03:16:01AM -0700, Jan Beulich wrote: > >>> On 15.01.19 at 10:44, <Paul.Durrant@xxxxxxxxxx> wrote: > >> -----Original Message----- > > [snip] > >> >> (XEN) Xen call trace: > >> >> (XEN) [<ffff82d08025ccbc>] iommu_map+0xba/0x176 > >> >> (XEN) [<ffff82d0804182d8>] iommu_hwdom_init+0xef/0x220 > >> >> (XEN) [<ffff82d08043716c>] dom0_construct_pvh+0x189/0x129e > >> >> (XEN) [<ffff82d08043e53c>] construct_dom0+0xd4/0xb14 > >> >> (XEN) [<ffff82d08042d8ef>] __start_xen+0x2710/0x2830 > >> >> (XEN) [<ffff82d0802000f3>] __high_start+0x53/0x55 > >> >> (XEN) > >> >> (XEN) > >> >> (XEN) **************************************** > >> >> (XEN) Panic on CPU 0: > >> >> (XEN) Assertion 'IS_ALIGNED(dfn_x(dfn), (1ul << page_order))' failed at > >> iommu.c:323 > >> >> (XEN) **************************************** > >> > > >> >Oh, this was added by Paul quite recently. You seem to be using a > >> >rather old commit (a5b0eb3636), is there any reason for using such an > >> >old baseline? > >> > >> I was using the master branch. Your patch below did fix this issue. > > > > Given this failure and the fact that valid orders differ between different > > architectures, I propose we change the argument to the iommu_map/unmap > > wrapper functions from an order to a count, thus making it clear that there > > is no alignment restriction. > > But the whole idea is for there to be an alignment restriction, such > that it is easy to determine whether large page mappings can be > used to satisfy the request. What's the exact case where a caller > absolutely has to pass in a mis-aligned (dfn,size) tuple? Taking PVH Dom0 builder as an example, it's possible to have a RAM region that starts on a 4K only aligned address. The natural operation in that case would be to try to allocate a memory region as big as possible up to the next 2MB boundary. Hence it would be valid to attempt to populate this 4K only aligned address using an order > 0 and < 9 (2MB order). The alternative here if the asserts are not removed would be to open-code a loop in the caller that iterates creating a bunch of order 0 mappings up to the 2MB boundary. The overhead in that case would be quite big, so I don't think we want to go down that route (also we would end up with a bunch of loops in the callers). Thanks, Roger. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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