On 15.11.2008, at 14:03, Andi Kleen wrote:
"Serebrin, Benjamin (Calendar)" <[EMAIL PROTECTED]>
writes:
64-bit OSes will use SYSCALL for 64-bit code. CPUID name string
should
be "FakeCPUFakeCPU"
One problem is that you'll disable a lot of vendor specific setup
code if you do that. Might have all kinds of unexpected side effects.
Yes, but since we're emulating a CPU anyways we don't want vendor
specific setup, since we might live migrate. And quirks should already
be handled by the host. We'd only nop them out usually.
Also it might break user space, unless you key the fake vendor CPUID
intercept on ring 0 vs ring 3 (but even if that might not be enough
because some kernel modules can call CPUID on their own)
Is there userspace code that relies on GenuineIntel? What would a new
vendor do? Can't we just behave the same and have our self-invented
vendor string added to applications that direly need to know which
vendor they're running on?
I think just emulating SYSCALL/SYSENTER would be safer. It shouldn't
be that much slower than int 0x80 hopefully.
Well emulating them means you're leaving the VM on every user<->kernel
transition. That's a _huge_ performance hit. I don't have the numbers,
but IIRC a roundtrip is ~3000 cycles.
So yes, it definitely is safer. But it'll hurt performance a lot -
which is exactly what you'd want to avoid when migrating between
vendors.
Alex
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