Re: [Xen-devel] Failed vm entry with heavy use of emulator

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.09.16 at 07:59, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> On 09/07/16 02:31, Tamas K Lengyel wrote:
>> Just a quick update on this issue, I also now see the following
>> emulation error when I use xen-access with the emulation response for
>> the exec case. The issue previously reported with the failed vm entry
>> seem to happen only when emulating in response to the write-access.
>> 
>> (XEN) Mem event emulation failed: d5v1 32bit @ 0008:826c602c -> 0f 21
>> c0 89 82 dc 02 00 00 0f 21 c8 89 82 e0 02
>> (XEN) Mem event emulation failed: d5v0 32bit @ 0008:82678caa -> cf 90
>> f7 45 70 00 00 02 00 75 09 f7 45 6c 01 00
>> (XEN) d5v1 Triple fault - invoking HVM shutdown action
>> (XEN) *** Dumping Dom5 vcpu#1 state: ***
>> (XEN) ----[ Xen-4.7.0  x86_64  debug=n  Not tainted ]----
>> (XEN) CPU:    6
>> (XEN) RIP:    0008:[<00000000827194f8>]
>> (XEN) RFLAGS: 0000000000014292   CONTEXT: hvm guest (d5v1)
>> (XEN) rax: 00000000badb10cc   rbx: 00000000807c1534   rcx: 0000000000000000
>> (XEN) rdx: 0000000000000000   rsi: 000000008271957f   rdi: 00000000badb10cc
>> (XEN) rbp: 00000000807c10e4   rsp: 00000000807c0d30   r8:  0000000000000000
>> (XEN) r9:  0000000000000000   r10: 0000000000000000   r11: 0000000000000000
>> (XEN) r12: 0000000000000000   r13: 0000000000000000   r14: 0000000000000000
>> (XEN) r15: 0000000000000000   cr0: 000000008001003b   cr4: 00000000000406f9
>> (XEN) cr3: 0000000000185000   cr2: 00000000807c0d2c
>> (XEN) ds: 0023   es: 0023   fs: 0030   gs: 0000   ss: 0010   cs: 0008
> 
> I see that there were two failed emulation attempts previously (most
> likely there's no support in the emulator for the listed instructions).

The first one would have support in the emulator (it's a DR0 access),
if the read_dr() hook was set (which it looks like isn't the case, but
should be easy to fix).

The second one (IRET) currently gets handled by the emulator only
when the guest is in real mode.

Jan


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