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

On 24/06/13 13:52, Jan Beulich wrote:
On 24.06.13 at 12:10, George Dunlap <george.dunlap@xxxxxxxxxxxxx> 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@xxxxxxxxx>.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
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.


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