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>

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.

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;
 }

include/exec/cpu-all.h

@@ -328,7 +328,18 @@ CPUArchState *cpu_copy(CPUArchState *env);
      | CPU_INTERRUPT_TGT_EXT_3   \
      | CPU_INTERRUPT_TGT_EXT_4)
 
-#if !defined(CONFIG_USER_ONLY)
+#ifdef CONFIG_USER_ONLY
+
+/*
+ * Allow some level of source compatibility with softmmu.  We do not
+ * support any of the more exotic features, so only invalid pages may
+ * be signaled by probe_access_flags().
+ */
+#define TLB_INVALID_MASK    (1 << (TARGET_PAGE_BITS_MIN - 1))
+#define TLB_MMIO            0
+#define TLB_WATCHPOINT      0
+
+#else
 
 /*
  * Flags stored in the low bits of the TLB virtual address.

include/exec/exec-all.h

@@ -362,6 +362,28 @@ static inline void *probe_read(CPUArchState *env, target_ulong addr, int size,
     return probe_access(env, addr, size, MMU_DATA_LOAD, mmu_idx, retaddr);
 }
 
+/**
+ * probe_access_flags:
+ * @env: CPUArchState
+ * @addr: guest virtual address to look up
+ * @access_type: read, write or execute permission
+ * @mmu_idx: MMU index to use for lookup
+ * @nonfault: suppress the fault
+ * @phost: return value for host address
+ * @retaddr: return address for unwinding
+ *
+ * Similar to probe_access, loosely returning the TLB_FLAGS_MASK for
+ * the page, and storing the host address for RAM in @phost.
+ *
+ * If @nonfault is set, do not raise an exception but return TLB_INVALID_MASK.
+ * Do not handle watchpoints, but include TLB_WATCHPOINT in the returned flags.
+ * Do handle clean pages, so exclude TLB_NOTDIRY from the returned flags.
+ * For simplicity, all "mmio-like" flags are folded to TLB_MMIO.
+ */
+int probe_access_flags(CPUArchState *env, target_ulong addr,
+                       MMUAccessType access_type, int mmu_idx,
+                       bool nonfault, void **phost, uintptr_t retaddr);
+
 #define CODE_GEN_ALIGN           16 /* must be >= of the size of a icache line */
 
 /* Estimated block size for TB allocation.  */