On Wed, 25 Mar 2020 at 20:49, Laszlo Ersek <ler...@redhat.com> wrote: > > On 03/25/20 16:29, Ard Biesheuvel wrote: > > The new ArmMmuLib code is easier to reason about, so that is what I did: > > currently, when we create mappings that cover existing table entries, we > > may end up overwriting those with block entries without taking the mapping > > attributes of the original table entries into account. So let's fix this. > > > > I honestly don't know whether the original code was better at dealing with > > this: I do remember some changes from Heyi that may have been related, but > > the old code is not easy to follow. In any case, I didn't manage to hit this > > case in practice, given that we typically start out with large mappings, and > > break them down later (to set permissions), rather than the other way > > around. > > > > Patch #1 adds some helpers to hide the insane way the type bits change > > meaning when you change to level 3. > > > > Patch #2 ensures that we only replace (and free) table entries with block > > entries if it is guaranteed that doing so will not lose any attribute > > information. > > > > Changes since v2: > > - add patch to limit recursion to levels < 3 in FreePageTablesRecursive() > > > > Changes since v1: > > - zero newly allocated pages before splitting a block entry into a table > > entry, to avoid garbage in that page being misidentified as entry type > > attributes - this should fix the crash observed by Laszlo > > > > Cc: Laszlo Ersek <ler...@redhat.com> > > Cc: Leif Lindholm <l...@nuviainc.com> > > Cc: Ashish Singhal <ashishsin...@nvidia.com> > > > > Ard Biesheuvel (3): > > ArmPkg/ArmMmuLib AARCH64: limit recursion when freeing page tables > > ArmPkg/ArmMmuLib AARCH64: use helpers to determine table entry types > > ArmPkg/ArmMmuLib AARCH64: preserve attributes when replacing a table > > entry > > > > .../Library/ArmMmuLib/AArch64/ArmMmuLibCore.c | 83 +++++++++++++++---- > > 1 file changed, 68 insertions(+), 15 deletions(-) > > > > Tested-by: Laszlo Ersek <ler...@redhat.com> >
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