Messages in this thread | | | Subject | Re: [PATCHv2 1/3] x86/mm: Provide pmdp_establish() helper | From | Nadav Amit <> | Date | Mon, 19 Jun 2017 10:11:35 -0700 |
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Kirill A. Shutemov <kirill.shutemov@linux.intel.com> wrote:
> We need an atomic way to setup pmd page table entry, avoiding races with > CPU setting dirty/accessed bits. This is required to implement > pmdp_invalidate() that doesn't loose these bits. > > On PAE we have to use cmpxchg8b as we cannot assume what is value of new pmd and > setting it up half-by-half can expose broken corrupted entry to CPU.
...
> > +#ifndef pmdp_establish > +#define pmdp_establish pmdp_establish > +static inline pmd_t pmdp_establish(pmd_t *pmdp, pmd_t pmd) > +{ > + if (IS_ENABLED(CONFIG_SMP)) { > + return xchg(pmdp, pmd); > + } else { > + pmd_t old = *pmdp; > + *pmdp = pmd;
I think you may want to use WRITE_ONCE() here - otherwise nobody guarantees that the compiler will not split writes to *pmdp. Although the kernel uses similar code to setting PTEs and PMDs, I think that it is best to start fixing it. Obviously, you might need a different code path for 32-bit kernels.
Regards, Nadav
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