Re: [PATCH] make KVM conform to sucky rdmsr interface

Avi Kivity
2007-03-22T07:20:32Z

Rusty Russell wrote:
> Grrr.... Andi refused to take my "rdmsr64" patch which moved to a
> function-like interface for MSRs, dismissing it as pointless churn.
>
> paravirt_ops cleanups changed a macro to an inline and spotted this
> kvm bug.
>
> Signed-off-by: Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>
>
> diff -r 47c6ee74a5c5 drivers/kvm/vmx.c
> --- a/drivers/kvm/vmx.c Thu Mar 22 12:57:44 2007 +1100
> +++ b/drivers/kvm/vmx.c Thu Mar 22 13:38:24 2007 +1100
> @@ -1127,7 +1127,7 @@ static int vmx_vcpu_setup(struct kvm_vcp
> u64 data;
> int j = vcpu->nmsrs;
>
> - if (rdmsr_safe(index, &data_low, &data_high) < 0)
> + if (rdmsr_safe(index, data_low, data_high) < 0)
> continue;
> if (wrmsr_safe(index, data_low, data_high) < 0)
> continue;
>
>
>

My rdmsr_safe (x86_64, i386 is similar/same) is

#define rdmsr_safe(msr,a,b) \
({ int ret__; \
asm volatile ("1: rdmsr\n" \
"2:\n" \
".section .fixup,\"ax\"\n" \
"3: movl %4,%0\n" \
" jmp 2b\n" \
".previous\n" \
".section __ex_table,\"a\"\n" \
" .align 8\n" \
" .quad 1b,3b\n" \
".previous":"=&bDS" (ret__), "=a"(*(a)), "=d"(*(b))\
:"c"(msr), "i"(-EIO), "0"(0)); \
ret__; })

Which seems quite happy to accept pointers to the values. The one in
asm/i386/paravirt.h has a similar calling convention.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.