[PATCH v2 6/7] target/i386: remove unnecessary/wrong application of the A20 mask

[Paolo Bonzini]

If ptw_translate() does a MMU_PHYS_IDX access, the A20 mask is already
applied in get_physical_address(), which is called via probe_access_full()
and x86_cpu_tlb_fill().

If ptw_translate() on the other hand does a MMU_NESTED_IDX access,
the A20 mask must not be applied to the address that is looked up in
the nested page tables; it must be applied only to the addresses that
hold the NPT entries (which is achieved via MMU_PHYS_IDX, per the
previous paragraph).

Therefore, we can remove A20 masking from the computation of the page
table entry's address, and let get_physical_address() or mmu_translate()
apply it when they know they are returning a host-physical address.

Fixes: 4a1e9d4d11c ("target/i386: Use atomic operations for pte updates", 
2022-10-18)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target/i386/tcg/sysemu/excp_helper.c | 21 ++++++++-------------
 1 file changed, 8 insertions(+), 13 deletions(-)

diff --git a/target/i386/tcg/sysemu/excp_helper.c 
b/target/i386/tcg/sysemu/excp_helper.c
index 8bcdd2906d5..2ddc08b4bb6 100644
--- a/target/i386/tcg/sysemu/excp_helper.c
+++ b/target/i386/tcg/sysemu/excp_helper.c
@@ -164,8 +164,7 @@ static bool mmu_translate(CPUX86State *env, const 
TranslateParams *in,
                 /*
                  * Page table level 5
                  */
-                pte_addr = ((in->cr3 & ~0xfff) +
-                            (((addr >> 48) & 0x1ff) << 3)) & a20_mask;
+                pte_addr = (in->cr3 & ~0xfff) + (((addr >> 48) & 0x1ff) << 3);
                 if (!ptw_translate(&pte_trans, pte_addr)) {
                     return false;
                 }
@@ -189,8 +188,7 @@ static bool mmu_translate(CPUX86State *env, const 
TranslateParams *in,
             /*
              * Page table level 4
              */
-            pte_addr = ((pte & PG_ADDRESS_MASK) +
-                        (((addr >> 39) & 0x1ff) << 3)) & a20_mask;
+            pte_addr = (pte & PG_ADDRESS_MASK) + (((addr >> 39) & 0x1ff) << 3);
             if (!ptw_translate(&pte_trans, pte_addr)) {
                 return false;
             }
@@ -210,8 +208,7 @@ static bool mmu_translate(CPUX86State *env, const 
TranslateParams *in,
             /*
              * Page table level 3
              */
-            pte_addr = ((pte & PG_ADDRESS_MASK) +
-                        (((addr >> 30) & 0x1ff) << 3)) & a20_mask;
+            pte_addr = (pte & PG_ADDRESS_MASK) + (((addr >> 30) & 0x1ff) << 3);
             if (!ptw_translate(&pte_trans, pte_addr)) {
                 return false;
             }
@@ -238,7 +235,7 @@ static bool mmu_translate(CPUX86State *env, const 
TranslateParams *in,
             /*
              * Page table level 3
              */
-            pte_addr = ((in->cr3 & 0xffffffe0ULL) + ((addr >> 27) & 0x18)) & 
a20_mask;
+            pte_addr = (in->cr3 & 0xffffffe0ULL) + ((addr >> 27) & 0x18);
             if (!ptw_translate(&pte_trans, pte_addr)) {
                 return false;
             }
@@ -260,8 +257,7 @@ static bool mmu_translate(CPUX86State *env, const 
TranslateParams *in,
         /*
          * Page table level 2
          */
-        pte_addr = ((pte & PG_ADDRESS_MASK) +
-                    (((addr >> 21) & 0x1ff) << 3)) & a20_mask;
+        pte_addr = (pte & PG_ADDRESS_MASK) + (((addr >> 21) & 0x1ff) << 3);
         if (!ptw_translate(&pte_trans, pte_addr)) {
             return false;
         }
@@ -287,8 +283,7 @@ static bool mmu_translate(CPUX86State *env, const 
TranslateParams *in,
         /*
          * Page table level 1
          */
-        pte_addr = ((pte & PG_ADDRESS_MASK) +
-                    (((addr >> 12) & 0x1ff) << 3)) & a20_mask;
+        pte_addr = (pte & PG_ADDRESS_MASK) + (((addr >> 12) & 0x1ff) << 3);
         if (!ptw_translate(&pte_trans, pte_addr)) {
             return false;
         }
@@ -306,7 +301,7 @@ static bool mmu_translate(CPUX86State *env, const 
TranslateParams *in,
         /*
          * Page table level 2
          */
-        pte_addr = ((in->cr3 & 0xfffff000ULL) + ((addr >> 20) & 0xffc)) & 
a20_mask;
+        pte_addr = (in->cr3 & 0xfffff000ULL) + ((addr >> 20) & 0xffc);
         if (!ptw_translate(&pte_trans, pte_addr)) {
             return false;
         }
@@ -335,7 +330,7 @@ static bool mmu_translate(CPUX86State *env, const 
TranslateParams *in,
         /*
          * Page table level 1
          */
-        pte_addr = ((pte & ~0xfffu) + ((addr >> 10) & 0xffc)) & a20_mask;
+        pte_addr = (pte & ~0xfffu) + ((addr >> 10) & 0xffc);
         if (!ptw_translate(&pte_trans, pte_addr)) {
             return false;
         }
-- 
2.43.0