Message ID | 20220825202939.3041660-1-Liam.Howlett@oracle.com (mailing list archive) |
---|---|
State | New |
Headers | show |
Series | mm/mprotect: Fix maple tree start address in do_mprotect_pkey() | expand |
On Thu, 25 Aug 2022 20:30:24 +0000 Liam Howlett <liam.howlett@oracle.com> wrote:
> Use the untagged_addr() instead of the address passed into the function.
What are the runtime effects of this fix?
* Andrew Morton <akpm@linux-foundation.org> [220825 21:06]: > On Thu, 25 Aug 2022 20:30:24 +0000 Liam Howlett <liam.howlett@oracle.com> wrote: > > > Use the untagged_addr() instead of the address passed into the function. > > What are the runtime effects of this fix? Prior to my change to use the maple tree, the start address was changed before calling find_vma() with the untagged_addr() version of start. My first change recorded the tagged address and searched on the incorrect start location - which would have found the incorrect VMA. This fix will use the untagged_addr() as the start of the search as it was before I changed the code at all. Any penalty of calling untagged_addr() occurred regardless of the version that was used. The search of the maple tree would have also occurred in both versions - just at the wrong location before this fix. I expect that the execution time would be equal as the search on the tagged address would have either returned a VMA at start, or the VMA in the next slot in the maple tree node - probably immeasurably slower since the data is very likely already in the CPU cache, but I don't have hard data to say either way. I can look into a benchmark to measure the difference between both working versions, but I don't have an arm64 native target so it will be emulated.
diff --git a/mm/mprotect.c b/mm/mprotect.c index f2b9b1da9083..3c79796be65e 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -675,7 +675,7 @@ static int do_mprotect_pkey(unsigned long start, size_t len, const bool rier = (current->personality & READ_IMPLIES_EXEC) && (prot & PROT_READ); struct mmu_gather tlb; - MA_STATE(mas, ¤t->mm->mm_mt, start, start); + MA_STATE(mas, ¤t->mm->mm_mt, 0, 0); start = untagged_addr(start); @@ -707,6 +707,7 @@ static int do_mprotect_pkey(unsigned long start, size_t len, if ((pkey != -1) && !mm_pkey_is_allocated(current->mm, pkey)) goto out; + mas_set(&mas, start); vma = mas_find(&mas, ULONG_MAX); error = -ENOMEM; if (!vma)
Use the untagged_addr() instead of the address passed into the function. Fixes: 3338b715d25d (mm/mprotect: use maple tree navigation instead of vma linked list) Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com> --- mm/mprotect.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)