Virtualization - Apr 2007 - New CPUID/MSR driver; virtualization hooks

I have finally gotten off the pot and finished writing up my new 
CPUID/MSR driver, which contains support for registers that need 
arbitrary GPRs touched.  For i386 vs x86-64 compatibility, both use an 
x86-64 register image (16 64-bit register fields); this allows 32-bit 
userspace to access the full 64-bit image if the kernel is 64 bits.

Anyway, this presumably requires new paravirtualization hooks.  The 
patch is at:

http://www.kernel.org/pub/linux/kernel/people/hpa/new-cpuid-msr.patch

... and a git tree is at ...

http://git.kernel.org/?p=linux/kernel/git/hpa/linux-2.6-cpuidmsr.git;a=summary

I'm posting this here to give the paravirt maintainers an opportunity to 
comment.  Presumably the functions that need to be paravirtualized are 
the ones represented by the functions do_cpuid(), do_rdmsr() and 
do_wrmsr(): they take a cpu number, an input register image, and an 
output register image, and return either 0 or -EIO (in case of a trap.)

	-hpa

On Wed, Apr 04, 2007 at 05:50:58PM -0700, H. Peter Anvin
wrote:
> I have finally gotten off the pot and finished writing up my new 
> CPUID/MSR driver, which contains support for registers that need 
> arbitrary GPRs touched.  For i386 vs x86-64 compatibility, both use an 
> x86-64 register image (16 64-bit register fields); this allows 32-bit 
> userspace to access the full 64-bit image if the kernel is 64 bits.
> 
> Anyway, this presumably requires new paravirtualization hooks.  The 
> patch is at:
> 
> http://www.kernel.org/pub/linux/kernel/people/hpa/new-cpuid-msr.patch
I think you mean?

http://www.kernel.org/pub/linux/kernel/people/hpa/new-msr-cpuid.patch

Yours Tony

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* H. Peter Anvin (hpa@zytor.com) wrote:
> I have finally gotten off the pot and finished writing up my new 
> CPUID/MSR driver, which contains support for registers that need 
> arbitrary GPRs touched.  For i386 vs x86-64 compatibility, both use an 
> x86-64 register image (16 64-bit register fields); this allows 32-bit 
> userspace to access the full 64-bit image if the kernel is 64 bits.
> 
> Anyway, this presumably requires new paravirtualization hooks.  The 
> patch is at:
> 
> http://www.kernel.org/pub/linux/kernel/people/hpa/new-cpuid-msr.patch
Not mirrored out yet
> 
> ... and a git tree is at ...
> 
>
http://git.kernel.org/?p=linux/kernel/git/hpa/linux-2.6-cpuidmsr.git;a=summary
Bleah, and gitweb is unhappy ATM too.
> I'm posting this here to give the paravirt maintainers an opportunity
to
> comment.  Presumably the functions that need to be paravirtualized are 
> the ones represented by the functions do_cpuid(), do_rdmsr() and 
> do_wrmsr(): they take a cpu number, an input register image, and an 
> output register image, and return either 0 or -EIO (in case of a trap.)
Yes, so currently cpuid, for example, is like this:

do_cpuid
  cpuid
   __cpuid

Where __cpuid is
native_cpuid() on !CONFIG_PARAVIRT (include/asm-i386/processor.h)
(and this is real asm("cpuid"))
and
paravirt_ops.cpuid() on CONFIG_PARAVIRT (

Without having seen the patch yet, you'll need to make sure
that the final point which is issuing asm("cpuid") is wrapped
and split to CONFIG_PARAVIRT and non CONFIG_PARAVIRT modes.

Similar for rdmsr:

do_rdmsr
  rdmsr_eio
    rdmsr_safe

Where rdmsr is paravirtualized
rdmsr is asm("rdmsr") on !CONFIG_PARAVIRT (include/asm-i386/msr.h)
and
paravirt_ops.read_msr() on CONFIG_PARAVIRT (include/asm-i386/paravirt.h)

Similar for do_wrmsr.

Does that answer your question?

thanks,
-chris

H. Peter Anvin wrote:
> I have finally gotten off the pot and finished writing up my new 
> CPUID/MSR driver, which contains support for registers that need 
> arbitrary GPRs touched.  For i386 vs x86-64 compatibility, both use an 
> x86-64 register image (16 64-bit register fields); this allows 32-bit 
> userspace to access the full 64-bit image if the kernel is 64 bits.
>
> Anyway, this presumably requires new paravirtualization hooks.  The 
> patch is at:
>
> http://www.kernel.org/pub/linux/kernel/people/hpa/new-cpuid-msr.patch
>   
The requested URL /pub/linux/kernel/people/hpa/new-cpuid-msr.patch was 
not found on this server.
> ... and a git tree is at ...
>
>
http://git.kernel.org/?p=linux/kernel/git/hpa/linux-2.6-cpuidmsr.git;a=summary
>
> I'm posting this here to give the paravirt maintainers an opportunity
to
> comment.  Presumably the functions that need to be paravirtualized are 
> the ones represented by the functions do_cpuid(), do_rdmsr() and
>   
rdmsr / wrmsr can be dropped from paravirt-ops; at least for us (they 
will trap and emulate just fine, and this driver is not performance 
critical), and I think for the others as well.  CPUID, however, does 
require a hook.

Zach