Messages in this thread | | | Subject | Re: [PATCH v8 11/27] x86/mm: Introduce _PAGE_DIRTY_SW | From | Yu-cheng Yu <> | Date | Tue, 27 Aug 2019 15:37:12 -0700 |
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On Fri, 2019-08-23 at 16:02 +0200, Peter Zijlstra wrote: > On Tue, Aug 13, 2019 at 01:52:09PM -0700, Yu-cheng Yu wrote: > > > +static inline pte_t pte_move_flags(pte_t pte, pteval_t from, pteval_t to) > > +{ > > + if (pte_flags(pte) & from) > > + pte = pte_set_flags(pte_clear_flags(pte, from), to); > > + return pte; > > +} > > Aside of the whole conditional thing (I agree it would be better to have > this unconditionally); the function doesn't really do as advertised. > > That is, if @from is clear, it doesn't endeavour to make sure @to is > also clear. > > Now it might be sufficient, but in that case it really needs a comment > and or different name. > > An implementation that actually moves the bit is something like: > > pteval_t a,b; > > a = native_pte_value(pte); > b = (a >> from_bit) & 1; > a &= ~((1ULL << from_bit) | (1ULL << to_bit)); > a |= b << to_bit; > return make_native_pte(a);
There can be places calling pte_wrprotect() on a PTE that is already RO + DIRTY_SW. Then in pte_move_flags(pte, _PAGE_DIRTY_HW, _PAGE_DIRTY_SW) we do not want to clear _PAGE_DIRTY_SW. But, I will look into this and make it more obvious.
Thanks, Yu-cheng
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