On Mon, 2018-02-05 at 15:03 +0000, Ben Hutchings wrote: [...] > It certainly is too big a hammer. > > I think what's going wrong is that the pmd containing the fixmap area > is already mapped with _KERNPG_TABLE, i.e. excluding _PAGE_USER. Then > when we map the ptes for the pvclock area we don't update the pmd > protections. > > I'll look at some other branches to see how this was addressed there. [...] I ended up backporting most of the vDSO pvclock changes up to 4.5, as was done in 4.4-stable. This removes the need for the vDSO to access the pvclock fixmap. I picked these commits: e6577a7ce99a x86, vdso: Move the vvar area before the vdso text 73459e2a1ada x86: pvclock: Really remove the sched notifier for cross-cpu migrations 6b078f5de7fc x86, vdso, pvclock: Simplify and speed up the vdso pvclock reader dac16fba6fc5 x86/vdso: Get pvclock data from the vvar VMA instead of the fixmap and then applied your revert to re-enable use of pvclock. Ben. -- Ben Hutchings Beware of programmers who carry screwdrivers. - Leonard Brandwein
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