mm/mprotect: fix maple tree start address in do_mprotect_pkey()

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.

Use the untagged_addr() instead of the address passed into the function.

Link: https://lkml.kernel.org/r/20220825202939.3041660-1-Liam.Howlett@oracle.com
Fixes: 3338b715d25d ("mm/mprotect: use maple tree navigation instead of vma linked list")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 4549f5945ebe46a318edebf4cccd6b7daa3d5e4c..461dcbd4f21a6f9aa2aa910cad8ccaa7ec6dc0ea 100644 (file)
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -676,7 +676,7 @@ 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, &current->mm->mm_mt, start, start);
+       MA_STATE(mas, &current->mm->mm_mt, 0, 0);
 
        start = untagged_addr(start);
 
@@ -708,6 +708,7 @@ 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)