[PATCH 1/3] accel/tcg: Fix unaligned stores to s390x low-address-protected lowcore

[Ilya Leoshkevich]

If low-address-protection is active, unaligned stores to non-protected
parts of lowcore lead to protection exceptions. The reason is that in
such cases tlb_fill() call in store_helper_unaligned() covers
[0, addr + size) range, which contains the protected portion of
lowcore. This range is too large.

The most straightforward fix would be to make sure we stay within the
original [addr, addr + size) range. However, if an unaligned access
affects a single page, we don't need to call tlb_fill() in
store_helper_unaligned() at all, since it would be identical to
the previous tlb_fill() call in store_helper(), and therefore a no-op.
If an unaligned access covers multiple pages, this situation does not
occur.

Therefore simply skip TLB handling in store_helper_unaligned() if we
are dealing with a single page.

Fixes: 2bcf018340cb ("s390x/tcg: low-address protection support")
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 accel/tcg/cputlb.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/accel/tcg/cputlb.c b/accel/tcg/cputlb.c
index f90f4312ea..a46f3a654d 100644
--- a/accel/tcg/cputlb.c
+++ b/accel/tcg/cputlb.c
@@ -2248,7 +2248,7 @@ store_helper_unaligned(CPUArchState *env, target_ulong 
addr, uint64_t val,
     const size_t tlb_off = offsetof(CPUTLBEntry, addr_write);
     uintptr_t index, index2;
     CPUTLBEntry *entry, *entry2;
-    target_ulong page2, tlb_addr, tlb_addr2;
+    target_ulong page1, page2, tlb_addr, tlb_addr2;
     MemOpIdx oi;
     size_t size2;
     int i;
@@ -2256,15 +2256,17 @@ store_helper_unaligned(CPUArchState *env, target_ulong 
addr, uint64_t val,
     /*
      * Ensure the second page is in the TLB.  Note that the first page
      * is already guaranteed to be filled, and that the second page
-     * cannot evict the first.
+     * cannot evict the first.  An exception to this rule is PAGE_WRITE_INV
+     * handling: the first page could have evicted itself.
      */
+    page1 = addr & TARGET_PAGE_MASK;
     page2 = (addr + size) & TARGET_PAGE_MASK;
     size2 = (addr + size) & ~TARGET_PAGE_MASK;
     index2 = tlb_index(env, mmu_idx, page2);
     entry2 = tlb_entry(env, mmu_idx, page2);
 
     tlb_addr2 = tlb_addr_write(entry2);
-    if (!tlb_hit_page(tlb_addr2, page2)) {
+    if (page1 != page2 && !tlb_hit_page(tlb_addr2, page2)) {
         if (!victim_tlb_hit(env, mmu_idx, index2, tlb_off, page2)) {
             tlb_fill(env_cpu(env), page2, size2, MMU_DATA_STORE,
                      mmu_idx, retaddr);
-- 
2.35.3