>>> On 25.06.15 at 15:52, <paul.durr...@citrix.com> wrote: >> -----Original Message----- >> From: Jan Beulich [mailto:jbeul...@suse.com] >> Sent: 25 June 2015 14:48 >> To: Paul Durrant >> Cc: Andrew Cooper; xen-de...@lists.xenproject.org; Keir (Xen.org) >> Subject: RE: [PATCH v4 07/17] x86/hvm: add length to mmio check op >> >> >>> On 25.06.15 at 15:36, <paul.durr...@citrix.com> wrote: >> > I think that also allows me to simplfy the patch since I don't have to >> > modify the mmio_check op any more. I simply call it once for the first byte >> > of the access and, if it accepts, verify that it also accepts the last byte >> > of the access. >> >> That's actually not (generally) okay: There could be a hole in the >> middle. But as long as instructions don't do accesses wider than >> a page, we're fine with that in practice I think. Or wait, no, in the >> MSI-X this could not be okay: A 64-byte read to the 16 bytes >> 32 bytes away from a page boundary (and being the last entry >> on one device's MSI-X table) would extend into another device's >> MSI-X table on the next page. I.e. first and last bytes would be >> okay to be accessed, but bytes 16...31 of the access wouldn't. >> Of course the MSI-X read/write handlers don't currently permit >> such wide accesses, but anyway... > > We could also verify that, for a rep op, all reads/writes come back with > OKAY. I think that would be ok.
I wasn't thinking of a rep op, but of an AVX-512 memory access. Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
