Re: [PATCH 3/16] read/write_crX, clts and wbinvd for 64-bit paravirt

Jeremy Fitzhardinge
2007-11-01T15:30:59Z

Glauber de Oliveira Costa wrote:
> I in fact have seen bugs with mixed reads and writes to the same cr,
> (cr4), but adding the volatile
> flag to the read function seemed to fix it.

Well, volatile will make a read be repeated rather than caching the
previous value, but it has no effect on ordering.

> Yet, I agree with you that
> the theorectical problem exists for the reorder, and your proposed fix
> seems fine (although if we're really desperate about memory usage, we
> can use a char instead a int and save 3 bytes!)

Sure. Ideally the compiler would never even generate a reference to it,
and it could just be extern, but in practice the compiler will generate
references sometimes.

J

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