On 01/07/2012 12:26 PM, Stefan Hajnoczi wrote:
> An Ubuntu 9.10 Karmic Koala guest is unable to boot or install due to
> missing movdqa emulation:
>
> kvm_exit: reason EXCEPTION_NMI rip 0x7fef3e025a7b info 7fef3e799000 80000b0e
> kvm_page_fault: address 7fef3e799000 error_code f
> kvm_emulate_insn: 0:7fef3e025a7b: 66 0f 7f 07 (prot64)
Install udis86 (and udsi86-devel) and build trace-cmd; it will decode
the opcode for you.
>
> movdqa %xmm0,(%rdi)
>
> This patch adds movdqa to the emulator but does not implement #GP when
> the memory operand is unaligned to 16 bytes. I'm not sure whether
> alignment checking can be implemented as an opcode .flag or if it needs
> to be done in em_movdqa().
It should actually be automatic when the Sse flag is present, since it's
the norm for almost all SSE instructions. There should be a .flag to
override it for movdqu.
> A more fundamental question: why do we have to emulate this guest
> userspace SSE instruction in the first place? This host machine lacks
> EPT but can't we service the page fault and then retry execution inside
> the guest?
Not when the target is mmio - there is no possible mapping. With your
patch, is there a kvm_mmio trace right after the movdqa emulation?
>
> +static int em_movdqa(struct x86_emulate_ctxt *ctxt)
> +{
> + /* TODO alignment */
> + memcpy(&ctxt->dst.vec_val, &ctxt->src.vec_val, ctxt->op_bytes);
> + return X86EMUL_CONTINUE;
> +}
em_mov() should be adjusted to work here.
> +
> static int em_movdqu(struct x86_emulate_ctxt *ctxt)
> {
> memcpy(&ctxt->dst.vec_val, &ctxt->src.vec_val, ctxt->op_bytes);
> @@ -3115,7 +3122,7 @@ static struct opcode group11[] = {
> };
>
> static struct gprefix pfx_0f_6f_0f_7f = {
> - N, N, N, I(Sse, em_movdqu),
> + N, I(Sse, em_movdqa), N, I(Sse, em_movdqu),
> };
>
Need the Mov flag too (I see it's missing for movdqu as well); otherwise
the emulator will RMW the destination.
Don't forget a unit test (for both the aligned and unaligned case).
--
error compiling committee.c: too many arguments to function
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