accel/tcg: Add probe_access_flags

This new interface will allow targets to probe for a page
and then handle watchpoints themselves.  This will be most
useful for vector predicated memory operations, where one
page lookup can be used for many operations, and one test
can avoid many watchpoint checks.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200508154359.7494-6-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

2 files changed, 114 insertions, 86 deletions

diff --git a/accel/tcg/cputlb.c b/accel/tcg/cputlb.c
index e3b5750c3b..c708e9785f 100644
--- a/accel/tcg/cputlb.c
+++ b/accel/tcg/cputlb.c
@@ -1231,131 +1231,134 @@ static void notdirty_write(CPUState *cpu, vaddr mem_vaddr, unsigned size,
     }
 }
 
-/*
- * Probe for whether the specified guest access is permitted. If it is not
- * permitted then an exception will be taken in the same way as if this
- * were a real access (and we will not return).
- * If the size is 0 or the page requires I/O access, returns NULL; otherwise,
- * returns the address of the host page similar to tlb_vaddr_to_host().
- */
-void *probe_access(CPUArchState *env, target_ulong addr, int size,
-                   MMUAccessType access_type, int mmu_idx, uintptr_t retaddr)
+static int probe_access_internal(CPUArchState *env, target_ulong addr,
+                                 int fault_size, MMUAccessType access_type,
+                                 int mmu_idx, bool nonfault,
+                                 void **phost, uintptr_t retaddr)
 {
     uintptr_t index = tlb_index(env, mmu_idx, addr);
     CPUTLBEntry *entry = tlb_entry(env, mmu_idx, addr);
-    target_ulong tlb_addr;
+    target_ulong tlb_addr, page_addr;
     size_t elt_ofs;
-    int wp_access;
-
-    g_assert(-(addr | TARGET_PAGE_MASK) >= size);
+    int flags;
 
     switch (access_type) {
     case MMU_DATA_LOAD:
         elt_ofs = offsetof(CPUTLBEntry, addr_read);
-        wp_access = BP_MEM_READ;
         break;
     case MMU_DATA_STORE:
         elt_ofs = offsetof(CPUTLBEntry, addr_write);
-        wp_access = BP_MEM_WRITE;
         break;
     case MMU_INST_FETCH:
         elt_ofs = offsetof(CPUTLBEntry, addr_code);
-        wp_access = BP_MEM_READ;
         break;
     default:
         g_assert_not_reached();
     }
     tlb_addr = tlb_read_ofs(entry, elt_ofs);
 
-    if (unlikely(!tlb_hit(tlb_addr, addr))) {
-        if (!victim_tlb_hit(env, mmu_idx, index, elt_ofs,
-                            addr & TARGET_PAGE_MASK)) {
-            tlb_fill(env_cpu(env), addr, size, access_type, mmu_idx, retaddr);
-            /* TLB resize via tlb_fill may have moved the entry. */
-            index = tlb_index(env, mmu_idx, addr);
+    page_addr = addr & TARGET_PAGE_MASK;
+    if (!tlb_hit_page(tlb_addr, page_addr)) {
+        if (!victim_tlb_hit(env, mmu_idx, index, elt_ofs, page_addr)) {
+            CPUState *cs = env_cpu(env);
+            CPUClass *cc = CPU_GET_CLASS(cs);
+
+            if (!cc->tlb_fill(cs, addr, fault_size, access_type,
+                              mmu_idx, nonfault, retaddr)) {
+                /* Non-faulting page table read failed.  */
+                *phost = NULL;
+                return TLB_INVALID_MASK;
+            }
+
+            /* TLB resize via tlb_fill may have moved the entry.  */
             entry = tlb_entry(env, mmu_idx, addr);
         }
         tlb_addr = tlb_read_ofs(entry, elt_ofs);
     }
+    flags = tlb_addr & TLB_FLAGS_MASK;
 
-    if (!size) {
-        return NULL;
+    /* Fold all "mmio-like" bits into TLB_MMIO.  This is not RAM.  */
+    if (unlikely(flags & ~(TLB_WATCHPOINT | TLB_NOTDIRTY))) {
+        *phost = NULL;
+        return TLB_MMIO;
     }
 
-    if (unlikely(tlb_addr & TLB_FLAGS_MASK)) {
+    /* Everything else is RAM. */
+    *phost = (void *)((uintptr_t)addr + entry->addend);
+    return flags;
+}
+
+int probe_access_flags(CPUArchState *env, target_ulong addr,
+                       MMUAccessType access_type, int mmu_idx,
+                       bool nonfault, void **phost, uintptr_t retaddr)
+{
+    int flags;
+
+    flags = probe_access_internal(env, addr, 0, access_type, mmu_idx,
+                                  nonfault, phost, retaddr);
+
+    /* Handle clean RAM pages.  */
+    if (unlikely(flags & TLB_NOTDIRTY)) {
+        uintptr_t index = tlb_index(env, mmu_idx, addr);
         CPUIOTLBEntry *iotlbentry = &env_tlb(env)->d[mmu_idx].iotlb[index];
 
-        /* Reject I/O access, or other required slow-path.  */
-        if (tlb_addr & (TLB_MMIO | TLB_BSWAP | TLB_DISCARD_WRITE)) {
-            return NULL;
-        }
+        notdirty_write(env_cpu(env), addr, 1, iotlbentry, retaddr);
+        flags &= ~TLB_NOTDIRTY;
+    }
+
+    return flags;
+}
+
+void *probe_access(CPUArchState *env, target_ulong addr, int size,
+                   MMUAccessType access_type, int mmu_idx, uintptr_t retaddr)
+{
+    void *host;
+    int flags;
+
+    g_assert(-(addr | TARGET_PAGE_MASK) >= size);
+
+    flags = probe_access_internal(env, addr, size, access_type, mmu_idx,
+                                  false, &host, retaddr);
+
+    /* Per the interface, size == 0 merely faults the access. */
+    if (size == 0) {
+        return NULL;
+    }
+
+    if (unlikely(flags & (TLB_NOTDIRTY | TLB_WATCHPOINT))) {
+        uintptr_t index = tlb_index(env, mmu_idx, addr);
+        CPUIOTLBEntry *iotlbentry = &env_tlb(env)->d[mmu_idx].iotlb[index];
 
         /* Handle watchpoints.  */
-        if (tlb_addr & TLB_WATCHPOINT) {
+        if (flags & TLB_WATCHPOINT) {
+            int wp_access = (access_type == MMU_DATA_STORE
+                             ? BP_MEM_WRITE : BP_MEM_READ);
             cpu_check_watchpoint(env_cpu(env), addr, size,
                                  iotlbentry->attrs, wp_access, retaddr);
         }
 
         /* Handle clean RAM pages.  */
-        if (tlb_addr & TLB_NOTDIRTY) {
-            notdirty_write(env_cpu(env), addr, size, iotlbentry, retaddr);
+        if (flags & TLB_NOTDIRTY) {
+            notdirty_write(env_cpu(env), addr, 1, iotlbentry, retaddr);
         }
     }
 
-    return (void *)((uintptr_t)addr + entry->addend);
+    return host;
 }
 
 void *tlb_vaddr_to_host(CPUArchState *env, abi_ptr addr,
                         MMUAccessType access_type, int mmu_idx)
 {
-    CPUTLBEntry *entry = tlb_entry(env, mmu_idx, addr);
-    target_ulong tlb_addr, page;
-    size_t elt_ofs;
-
-    switch (access_type) {
-    case MMU_DATA_LOAD:
-        elt_ofs = offsetof(CPUTLBEntry, addr_read);
-        break;
-    case MMU_DATA_STORE:
-        elt_ofs = offsetof(CPUTLBEntry, addr_write);
-        break;
-    case MMU_INST_FETCH:
-        elt_ofs = offsetof(CPUTLBEntry, addr_code);
-        break;
-    default:
-        g_assert_not_reached();
-    }
+    void *host;
+    int flags;
 
-    page = addr & TARGET_PAGE_MASK;
-    tlb_addr = tlb_read_ofs(entry, elt_ofs);
-
-    if (!tlb_hit_page(tlb_addr, page)) {
-        uintptr_t index = tlb_index(env, mmu_idx, addr);
-
-        if (!victim_tlb_hit(env, mmu_idx, index, elt_ofs, page)) {
-            CPUState *cs = env_cpu(env);
-            CPUClass *cc = CPU_GET_CLASS(cs);
+    flags = probe_access_internal(env, addr, 0, access_type,
+                                  mmu_idx, true, &host, 0);
 
-            if (!cc->tlb_fill(cs, addr, 0, access_type, mmu_idx, true, 0)) {
-                /* Non-faulting page table read failed.  */
-                return NULL;
-            }
-
-            /* TLB resize via tlb_fill may have moved the entry.  */
-            entry = tlb_entry(env, mmu_idx, addr);
-        }
-        tlb_addr = tlb_read_ofs(entry, elt_ofs);
-    }
-
-    if (tlb_addr & ~TARGET_PAGE_MASK) {
-        /* IO access */
-        return NULL;
-    }
-
-    return (void *)((uintptr_t)addr + entry->addend);
+    /* No combination of flags are expected by the caller. */
+    return flags ? NULL : host;
 }
 
-
 #ifdef CONFIG_PLUGIN
 /*
  * Perform a TLB lookup and populate the qemu_plugin_hwaddr structure.
diff --git a/accel/tcg/user-exec.c b/accel/tcg/user-exec.c
index 03538e2a38..987342c50c 100644
--- a/accel/tcg/user-exec.c
+++ b/accel/tcg/user-exec.c
@@ -190,13 +190,12 @@ static inline int handle_cpu_signal(uintptr_t pc, siginfo_t *info,
     g_assert_not_reached();
 }
 
-void *probe_access(CPUArchState *env, target_ulong addr, int size,
-                   MMUAccessType access_type, int mmu_idx, uintptr_t retaddr)
+static int probe_access_internal(CPUArchState *env, target_ulong addr,
+                                 int fault_size, MMUAccessType access_type,
+                                 bool nonfault, uintptr_t ra)
 {
     int flags;
 
-    g_assert(-(addr | TARGET_PAGE_MASK) >= size);
-
     switch (access_type) {
     case MMU_DATA_STORE:
         flags = PAGE_WRITE;
@@ -212,12 +211,38 @@ void *probe_access(CPUArchState *env, target_ulong addr, int size,
     }
 
     if (!guest_addr_valid(addr) || page_check_range(addr, 1, flags) < 0) {
-        CPUState *cpu = env_cpu(env);
-        CPUClass *cc = CPU_GET_CLASS(cpu);
-        cc->tlb_fill(cpu, addr, size, access_type, MMU_USER_IDX, false,
-                     retaddr);
-        g_assert_not_reached();
+        if (nonfault) {
+            return TLB_INVALID_MASK;
+        } else {
+            CPUState *cpu = env_cpu(env);
+            CPUClass *cc = CPU_GET_CLASS(cpu);
+            cc->tlb_fill(cpu, addr, fault_size, access_type,
+                         MMU_USER_IDX, false, ra);
+            g_assert_not_reached();
+        }
     }
+    return 0;
+}
+
+int probe_access_flags(CPUArchState *env, target_ulong addr,
+                       MMUAccessType access_type, int mmu_idx,
+                       bool nonfault, void **phost, uintptr_t ra)
+{
+    int flags;
+
+    flags = probe_access_internal(env, addr, 0, access_type, nonfault, ra);
+    *phost = flags ? NULL : g2h(addr);
+    return flags;
+}
+
+void *probe_access(CPUArchState *env, target_ulong addr, int size,
+                   MMUAccessType access_type, int mmu_idx, uintptr_t ra)
+{
+    int flags;
+
+    g_assert(-(addr | TARGET_PAGE_MASK) >= size);
+    flags = probe_access_internal(env, addr, size, access_type, false, ra);
+    g_assert(flags == 0);
 
     return size ? g2h(addr) : NULL;
 }