Re: [PATCH v2 1/5] VMX: fix interaction of APIC-V and Viridian emulation

[George Dunlap <george.dunlap@eu.citrix.com>]

On 24/06/13 13:52, Jan Beulich wrote:
>>>> On 24.06.13 at 12:10, George Dunlap <george.dunlap@eu.citrix.com> wrote:
>> On 24/06/13 08:03, Jan Beulich wrote:
>>> Viridian using a synthetic MSR for issuing EOI notifications bypasses
>>> the normal in-processor handling, which would clear
>>> GUEST_INTR_STATUS.SVI. Hence we need to do this in software in order
>>> for future interrupts to get delivered.
>>>
>>> Based on analysis by Yang Z Zhang <yang.z.zhang@intel.com>.
>>>
>>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> Hmm... so there are three paths which may end up calling this vmx EOI
>> code -- from viridian.c:wrmsr_vidiridan_regs(), from
>> vlapic.c:vlapic_reg_write(), and vmx_handle_eoi_write().
> This is the very reason why I favored patch 2 over this one for
> 4.3 ...

Yes, I think I didn't realize that when I looked at the patch on 
Friday.  (It was the end of a very tiring week.)

What other operating systems have you tested patch #2 with?  IIRC Vista 
and Win7 both also have extensions, IIRC.  Also, has either #1 or #2 
been tested on AMD boxen?

Choosing #1 involves the risk that we've missed something an will make 
one of those three cases *not* like real hardware, which seems fairly 
small.  Choosing #2 involves the risk that MS may not have implemented 
the feature flag checking properly -- they almost surely test it *with* 
the feature flag much more than *without* it.  Even if they do test 
without it, they may not test with the particular combination of flags 
that we are proposing.

So overall, I still tend to think #1 is probably less risky.  But as I 
said, I'm willing to go with either one.

  -George