Messages in this thread | | | From | David Laight <> | Subject | RE: [RFC PATCH] x86/insn: support decode MOVSXD instruction for MMIO | Date | Fri, 31 Mar 2023 15:59:44 +0000 |
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From: Kirill A. Shutemov > Sent: 31 March 2023 16:25 ... > > No, SEV doesn't support userspace MMIO. > > But where do you filter out userspace MMIO? AFAICS, it goes straight from > from #VC to insn_decode_mmio(). Hm?
Probably by making vm_iomap_memory() fail.
Otherwise MOVSXD is the least of your problems. You'd need to worry about all the AVX opcodes as well.
Although you might even find kernel code that is using kernel_fpu_begin/end() to wrap mmio copies that use the big AVX512 registers. When each PCIe read takes about 1us (measured into our fpga) increasing the TLP to 64 bytes (from 8) makes a massive difference to buffer reads. (Mostly we try to get the fpga to do writes instead.)
David
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