On Wed, 2018-02-14 at 16:46 -0800, Jim Mattson wrote:
> On Wed, Feb 14, 2018 at 3:29 PM, David Woodhouse <dwmw@xxxxxxxxxxxx> wrote:
>
> > +#define alternative_msr_write(_msr, _val, _feature) \
> > + asm volatile(ALTERNATIVE("", \
> > + "movl %[msr], %%ecx\n\t" \
> > + "movl %[val], %%eax\n\t" \
> > + "movl $0, %%edx\n\t" \
> > + "wrmsr", \
> > + _feature) \
> > + : : [msr] "i" (_msr), [val] "i" (_val) \
> > + : "eax", "ecx", "edx", "memory")
> > +
>
> It's not needed now, but this would be more generally useful if the
> high 32 bits of the MSR value could also be specified.
Yeah, if we ever do want to make it completely generic then we could
move it from nospec-branch.h to alternative.h and make it possible to
set the high word. But for now I'm inclined not to overengineer it.
The idea *was* that Boris was going to bikeshed it away into some other
form, but having just reverted two of those patches I am less inclined
to accept any more of that kind of change that doesn't actually fix a
real bug.
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