On Mon, Nov 16, 2015 at 06:51:06PM +0100, =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= wrote:
> 2015-11-15 18:00+0200, Michael S. Tsirkin:
> > This patch adds a new parameter: eptp_switching_test, which enables
> >
> > testing EPT switching on VMX if supported by hardware. All EPT entries
> > are initialized to the same value so this adds no useful functionality
> > by itself, but can be used to test VMFUNC performance, and serve as a
> > basis for future features based on EPTP switching.
> >
> > Support for nested virt is not enabled.
> >
> > This was tested using the following code within guest:
> > #define VMX_VMFUNC ".byte 0x0f,0x01,0xd4"
> > static void vmfunc(unsigned int nr, unsigned int ept)
> > {
> > asm volatile(VMX_VMFUNC
> > :
> > : "a"(nr), "c"(ept)
> > : "memory");
> > }
> >
> > VMFUNC instruction cost was measured at ~122 cycles.
> > (Note: recent versions of gnu toolchain support
> > the vmfunc instruction - removing the need for writing
> > the bytecode manually).
> >
> > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > ---
> >
> > I think I'd like to put this upstream so future eptp switching work can
> > be implemented on top. Comments?
>
> I'd wait for the future. Patch is already on the list so people
> interested in benchmarking VMFUNC can quickly compile a kernel and
> developers will need to overwrite the code anyway.
It'll bitrot though. But I'll let Paolo decide that.
> (And I think that eptp switching is expected to be used in conjuction
> with #VE, so it'd then make sense to implement a nop for it as well.)
No idea how would I even test it, so I'm not interested in #VE at this
point. If you are - go ahead and post a patch for that on top though,
why not.
> > diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
> > @@ -3011,6 +3035,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
> > SECONDARY_EXEC_PAUSE_LOOP_EXITING |
> > SECONDARY_EXEC_RDTSCP |
> > SECONDARY_EXEC_ENABLE_INVPCID |
> > + SECONDARY_EXEC_ENABLE_VM_FUNCTIONS |
>
> The VMFUNC vmexit should be handled to prevent guests from triggering a
> WARN_ON on the host. (VMFUNC did just #UD before this patch.)
Do you mean VMFUNC other than EPTP switch 0? True, thanks!
>
> After that, it's ok for KVM.
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