[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH v14 00/20] Introduce PVH domU support

On 08/11/13 17:01, Tim Deegan wrote:
At 15:53 +0000 on 08 Nov (1383922404), George Dunlap wrote:
On 08/11/13 15:41, George Dunlap wrote:
On 04/11/13 17:34, Tim Deegan wrote:
At 17:23 +0000 on 04 Nov (1383582187), George Dunlap wrote:
On 04/11/13 16:59, Konrad Rzeszutek Wilk wrote:
This also means no support for "legacy" forced invalid ops -- only
cpuid is supported in this series.
(FWIW, support for legacy forced invalid ops was requested by Tim.)
I was worried about existing PV kernel code that used the fake-CPUID,
which would break if the 'core' kernel code went from PV to PVH.  But
I guess I could be convinced that such kernel code is buggy? Really,
the high-order bit was consistency.  The version I commented on
supported them for user-space but not for kernel, which seemed like
risking trouble for no benefit.
Oh right -- I think Mukesh we do need to support forced invalid ops
for user space so that we can use the same xen tools binaries on PV
and PVH kernels.

Hmm, Mukesh / Konrad, what tools are you actually thinking about
here?  Are these Oracle-specific tools?  I can't seem to find
XEN_CPUID or XEN_EMULATE_PREFIX anywhere in the tools/ directory of
the xen repo...
It's misc/xen-detect.c, for the curious (which helpfully does not use
the macros above).

Handling forced invalid ops it is, then.
The xen-detect code tries real CPUID first, so not supporting the fake
CPUID doesn't actually affect it at all.  That's why I could be
convinced that detection failures were a guest-side bug.

It would affect older code that _only_ tired the fake CPUID, or code
that for some reason needed to behave differently on PV vs HVM (though
it's not at all clear that on PVH such code should use the 'PV'

Yes, taking a closer look, xen-detect in a PVH domain will behave the same as in an HVM domain:

# ./xen-detect
Running in HVM context on Xen v4.4.

I don't think this is a big deal; to be robust your system should be able to operate properly in an HVM (or PVHVM) domU.

I'll leave this out for now, but I'll put a note in the cover letter and in the doc file so we don't forget about it.


Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.