[PULL 10/13] target/i386/tcg: use X86Access for TSS access

[Paolo Bonzini]

This takes care of probing the vaddr range in advance, and is also faster
because it avoids repeated TLB lookups.  It also matches the Intel manual
better, as it says "Checks that the current (old) TSS, new TSS, and all
segment descriptors used in the task switch are paged into system memory";
note however that it's not clear how the processor checks for segment
descriptors, and this check is not included in the AMD manual.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target/i386/tcg/seg_helper.c | 110 ++++++++++++++++++-----------------
 1 file changed, 58 insertions(+), 52 deletions(-)

diff --git a/target/i386/tcg/seg_helper.c b/target/i386/tcg/seg_helper.c
index 0242f9d8b58..fea08a2ba0f 100644
--- a/target/i386/tcg/seg_helper.c
+++ b/target/i386/tcg/seg_helper.c
@@ -27,6 +27,7 @@
 #include "exec/log.h"
 #include "helper-tcg.h"
 #include "seg_helper.h"
+#include "access.h"
 
 #ifdef TARGET_X86_64
 #define SET_ESP(val, sp_mask)                                   \
@@ -313,14 +314,15 @@ static int switch_tss_ra(CPUX86State *env, int 
tss_selector,
                          uint32_t e1, uint32_t e2, int source,
                          uint32_t next_eip, uintptr_t retaddr)
 {
-    int tss_limit, tss_limit_max, type, old_tss_limit_max, old_type, v1, v2, i;
+    int tss_limit, tss_limit_max, type, old_tss_limit_max, old_type, i;
     target_ulong tss_base;
     uint32_t new_regs[8], new_segs[6];
     uint32_t new_eflags, new_eip, new_cr3, new_ldt, new_trap;
     uint32_t old_eflags, eflags_mask;
     SegmentCache *dt;
-    int index;
+    int mmu_index, index;
     target_ulong ptr;
+    X86Access old, new;
 
     type = (e2 >> DESC_TYPE_SHIFT) & 0xf;
     LOG_PCALL("switch_tss: sel=0x%04x type=%d src=%d\n", tss_selector, type,
@@ -374,35 +376,45 @@ static int switch_tss_ra(CPUX86State *env, int 
tss_selector,
         raise_exception_err_ra(env, EXCP0A_TSS, tss_selector & 0xfffc, 
retaddr);
     }
 
+    /* X86Access avoids memory exceptions during the task switch */
+    mmu_index = cpu_mmu_index_kernel(env);
+    access_prepare_mmu(&old, env, env->tr.base, old_tss_limit_max,
+                       MMU_DATA_STORE, mmu_index, retaddr);
+
+    if (source == SWITCH_TSS_CALL) {
+        /* Probe for future write of parent task */
+        probe_access(env, tss_base, 2, MMU_DATA_STORE,
+                     mmu_index, retaddr);
+    }
+    access_prepare_mmu(&new, env, tss_base, tss_limit,
+                       MMU_DATA_LOAD, mmu_index, retaddr);
+
     /* read all the registers from the new TSS */
     if (type & 8) {
         /* 32 bit */
-        new_cr3 = cpu_ldl_kernel_ra(env, tss_base + 0x1c, retaddr);
-        new_eip = cpu_ldl_kernel_ra(env, tss_base + 0x20, retaddr);
-        new_eflags = cpu_ldl_kernel_ra(env, tss_base + 0x24, retaddr);
+        new_cr3 = access_ldl(&new, tss_base + 0x1c);
+        new_eip = access_ldl(&new, tss_base + 0x20);
+        new_eflags = access_ldl(&new, tss_base + 0x24);
         for (i = 0; i < 8; i++) {
-            new_regs[i] = cpu_ldl_kernel_ra(env, tss_base + (0x28 + i * 4),
-                                            retaddr);
+            new_regs[i] = access_ldl(&new, tss_base + (0x28 + i * 4));
         }
         for (i = 0; i < 6; i++) {
-            new_segs[i] = cpu_lduw_kernel_ra(env, tss_base + (0x48 + i * 4),
-                                             retaddr);
+            new_segs[i] = access_ldw(&new, tss_base + (0x48 + i * 4));
         }
-        new_ldt = cpu_lduw_kernel_ra(env, tss_base + 0x60, retaddr);
-        new_trap = cpu_ldl_kernel_ra(env, tss_base + 0x64, retaddr);
+        new_ldt = access_ldw(&new, tss_base + 0x60);
+        new_trap = access_ldl(&new, tss_base + 0x64);
     } else {
         /* 16 bit */
         new_cr3 = 0;
-        new_eip = cpu_lduw_kernel_ra(env, tss_base + 0x0e, retaddr);
-        new_eflags = cpu_lduw_kernel_ra(env, tss_base + 0x10, retaddr);
+        new_eip = access_ldw(&new, tss_base + 0x0e);
+        new_eflags = access_ldw(&new, tss_base + 0x10);
         for (i = 0; i < 8; i++) {
-            new_regs[i] = cpu_lduw_kernel_ra(env, tss_base + (0x12 + i * 2), 
retaddr);
+            new_regs[i] = access_ldw(&new, tss_base + (0x12 + i * 2));
         }
         for (i = 0; i < 4; i++) {
-            new_segs[i] = cpu_lduw_kernel_ra(env, tss_base + (0x22 + i * 2),
-                                             retaddr);
+            new_segs[i] = access_ldw(&new, tss_base + (0x22 + i * 2));
         }
-        new_ldt = cpu_lduw_kernel_ra(env, tss_base + 0x2a, retaddr);
+        new_ldt = access_ldw(&new, tss_base + 0x2a);
         new_segs[R_FS] = 0;
         new_segs[R_GS] = 0;
         new_trap = 0;
@@ -412,16 +424,6 @@ static int switch_tss_ra(CPUX86State *env, int 
tss_selector,
      chapters 12.2.5 and 13.2.4 on how to implement TSS Trap bit */
     (void)new_trap;
 
-    /* NOTE: we must avoid memory exceptions during the task switch,
-       so we make dummy accesses before */
-    /* XXX: it can still fail in some cases, so a bigger hack is
-       necessary to valid the TLB after having done the accesses */
-
-    v1 = cpu_ldub_kernel_ra(env, env->tr.base, retaddr);
-    v2 = cpu_ldub_kernel_ra(env, env->tr.base + old_tss_limit_max, retaddr);
-    cpu_stb_kernel_ra(env, env->tr.base, v1, retaddr);
-    cpu_stb_kernel_ra(env, env->tr.base + old_tss_limit_max, v2, retaddr);
-
     /* clear busy bit (it is restartable) */
     if (source == SWITCH_TSS_JMP || source == SWITCH_TSS_IRET) {
         tss_set_busy(env, env->tr.selector, 0, retaddr);
@@ -434,35 +436,35 @@ static int switch_tss_ra(CPUX86State *env, int 
tss_selector,
     /* save the current state in the old TSS */
     if (old_type & 8) {
         /* 32 bit */
-        cpu_stl_kernel_ra(env, env->tr.base + 0x20, next_eip, retaddr);
-        cpu_stl_kernel_ra(env, env->tr.base + 0x24, old_eflags, retaddr);
-        cpu_stl_kernel_ra(env, env->tr.base + (0x28 + 0 * 4), 
env->regs[R_EAX], retaddr);
-        cpu_stl_kernel_ra(env, env->tr.base + (0x28 + 1 * 4), 
env->regs[R_ECX], retaddr);
-        cpu_stl_kernel_ra(env, env->tr.base + (0x28 + 2 * 4), 
env->regs[R_EDX], retaddr);
-        cpu_stl_kernel_ra(env, env->tr.base + (0x28 + 3 * 4), 
env->regs[R_EBX], retaddr);
-        cpu_stl_kernel_ra(env, env->tr.base + (0x28 + 4 * 4), 
env->regs[R_ESP], retaddr);
-        cpu_stl_kernel_ra(env, env->tr.base + (0x28 + 5 * 4), 
env->regs[R_EBP], retaddr);
-        cpu_stl_kernel_ra(env, env->tr.base + (0x28 + 6 * 4), 
env->regs[R_ESI], retaddr);
-        cpu_stl_kernel_ra(env, env->tr.base + (0x28 + 7 * 4), 
env->regs[R_EDI], retaddr);
+        access_stl(&old, env->tr.base + 0x20, next_eip);
+        access_stl(&old, env->tr.base + 0x24, old_eflags);
+        access_stl(&old, env->tr.base + (0x28 + 0 * 4), env->regs[R_EAX]);
+        access_stl(&old, env->tr.base + (0x28 + 1 * 4), env->regs[R_ECX]);
+        access_stl(&old, env->tr.base + (0x28 + 2 * 4), env->regs[R_EDX]);
+        access_stl(&old, env->tr.base + (0x28 + 3 * 4), env->regs[R_EBX]);
+        access_stl(&old, env->tr.base + (0x28 + 4 * 4), env->regs[R_ESP]);
+        access_stl(&old, env->tr.base + (0x28 + 5 * 4), env->regs[R_EBP]);
+        access_stl(&old, env->tr.base + (0x28 + 6 * 4), env->regs[R_ESI]);
+        access_stl(&old, env->tr.base + (0x28 + 7 * 4), env->regs[R_EDI]);
         for (i = 0; i < 6; i++) {
-            cpu_stw_kernel_ra(env, env->tr.base + (0x48 + i * 4),
-                              env->segs[i].selector, retaddr);
+            access_stw(&old, env->tr.base + (0x48 + i * 4),
+                       env->segs[i].selector);
         }
     } else {
         /* 16 bit */
-        cpu_stw_kernel_ra(env, env->tr.base + 0x0e, next_eip, retaddr);
-        cpu_stw_kernel_ra(env, env->tr.base + 0x10, old_eflags, retaddr);
-        cpu_stw_kernel_ra(env, env->tr.base + (0x12 + 0 * 2), 
env->regs[R_EAX], retaddr);
-        cpu_stw_kernel_ra(env, env->tr.base + (0x12 + 1 * 2), 
env->regs[R_ECX], retaddr);
-        cpu_stw_kernel_ra(env, env->tr.base + (0x12 + 2 * 2), 
env->regs[R_EDX], retaddr);
-        cpu_stw_kernel_ra(env, env->tr.base + (0x12 + 3 * 2), 
env->regs[R_EBX], retaddr);
-        cpu_stw_kernel_ra(env, env->tr.base + (0x12 + 4 * 2), 
env->regs[R_ESP], retaddr);
-        cpu_stw_kernel_ra(env, env->tr.base + (0x12 + 5 * 2), 
env->regs[R_EBP], retaddr);
-        cpu_stw_kernel_ra(env, env->tr.base + (0x12 + 6 * 2), 
env->regs[R_ESI], retaddr);
-        cpu_stw_kernel_ra(env, env->tr.base + (0x12 + 7 * 2), 
env->regs[R_EDI], retaddr);
+        access_stw(&old, env->tr.base + 0x0e, next_eip);
+        access_stw(&old, env->tr.base + 0x10, old_eflags);
+        access_stw(&old, env->tr.base + (0x12 + 0 * 2), env->regs[R_EAX]);
+        access_stw(&old, env->tr.base + (0x12 + 1 * 2), env->regs[R_ECX]);
+        access_stw(&old, env->tr.base + (0x12 + 2 * 2), env->regs[R_EDX]);
+        access_stw(&old, env->tr.base + (0x12 + 3 * 2), env->regs[R_EBX]);
+        access_stw(&old, env->tr.base + (0x12 + 4 * 2), env->regs[R_ESP]);
+        access_stw(&old, env->tr.base + (0x12 + 5 * 2), env->regs[R_EBP]);
+        access_stw(&old, env->tr.base + (0x12 + 6 * 2), env->regs[R_ESI]);
+        access_stw(&old, env->tr.base + (0x12 + 7 * 2), env->regs[R_EDI]);
         for (i = 0; i < 4; i++) {
-            cpu_stw_kernel_ra(env, env->tr.base + (0x22 + i * 2),
-                              env->segs[i].selector, retaddr);
+            access_stw(&old, env->tr.base + (0x22 + i * 2),
+                       env->segs[i].selector);
         }
     }
 
@@ -470,7 +472,11 @@ static int switch_tss_ra(CPUX86State *env, int 
tss_selector,
        context */
 
     if (source == SWITCH_TSS_CALL) {
-        cpu_stw_kernel_ra(env, tss_base, env->tr.selector, retaddr);
+        /*
+         * Thanks to the probe_access above, we know the first two
+         * bytes addressed by &new are writable too.
+         */
+        access_stw(&new, tss_base, env->tr.selector);
         new_eflags |= NT_MASK;
     }
 
-- 
2.45.2