[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Xen-devel] Re: [PATCH 03 of 36] x86: add memory barriers to wrmsr

H. Peter Anvin wrote:
Arjan van de Ven wrote:
I suppose, though I would be inclined to put the barriers in the
wrmsr macro itself to act as documentation.

yeah I meant like this:

static inline void native_write_msr(unsigned int msr,
                     unsigned low, unsigned high)
    asm volatile("wrmsr" : : "c" (msr), "a"(low), "d" (high));

or in the same in the thing that calls this.

Actually, I believe the barrier(); before is actually incorrect, since it would affect the wrmsr() register arguments rather than the wrmsr instruction itself.

How so? What kind of failure do think might occur? Some effect on how the wrmsr arguments are evaluated?

barrier() is specifically a compiler optimisation barrier, so the barrier before would prevent the compiler from moving anything logically before the wrmsr to afterwards.

That said, making the wrmsr itself a memory clobber may be simpler understand with a comment, rather than separate barriers...


Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.