[Qemu-devel] [PATCH 05/25] exec: Resolve subpages in one step except for IOTLB fills

[Paolo Bonzini <pbonzini@redhat.com>]

From: Jan Kiszka <jan.kiszka@siemens.com>

Except for the case of setting the IOTLB entry in TCG mode, we can avoid
the subpage dispatching handlers and do the resolution directly on
address_space_lookup_region. An IOTLB entry describes a full page, not
only the region that the first access to a sub-divided page may return.

This patch therefore introduces a special translation function,
address_space_translate_for_iotlb, that avoids the subpage resolutions.
In contrast, callers of the existing address_space_translate service
will now always receive the terminal memory region section. This will be
important for breaking the BQL and for enabling unaligned memory region.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 cputlb.c              |  4 ++--
 exec.c                | 49 ++++++++++++++++++++++++++++++++++++-------------
 include/exec/cputlb.h |  4 ++++
 3 files changed, 42 insertions(+), 15 deletions(-)

diff --git a/cputlb.c b/cputlb.c
index 1230e9e..947f17c 100644
--- a/cputlb.c
+++ b/cputlb.c
@@ -256,8 +256,8 @@ void tlb_set_page(CPUArchState *env, target_ulong vaddr,
     }
 
     sz = size;
-    section = address_space_translate(&address_space_memory, paddr, &xlat, &sz,
-                                      false);
+    section = address_space_translate_for_iotlb(&address_space_memory, paddr,
+                                                &xlat, &sz);
     assert(sz >= TARGET_PAGE_SIZE);
 
 #if defined(DEBUG_TLB)
diff --git a/exec.c b/exec.c
index 9c6f1fe..a59abc7 100644
--- a/exec.c
+++ b/exec.c
@@ -97,6 +97,13 @@ struct AddressSpaceDispatch {
     MemoryListener listener;
 };
 
+#define SUBPAGE_IDX(addr) ((addr) & ~TARGET_PAGE_MASK)
+typedef struct subpage_t {
+    MemoryRegion iomem;
+    hwaddr base;
+    uint16_t sub_section[TARGET_PAGE_SIZE];
+} subpage_t;
+
 static MemoryRegionSection *phys_sections;
 static unsigned phys_sections_nb, phys_sections_nb_alloc;
 static uint16_t phys_section_unassigned;
@@ -220,19 +227,28 @@ bool memory_region_is_unassigned(MemoryRegion *mr)
 }
 
 static MemoryRegionSection *address_space_lookup_region(AddressSpace *as,
-                                                        hwaddr addr)
+                                                        hwaddr addr,
+                                                        bool resolve_subpage)
 {
-    return phys_page_find(as->dispatch, addr >> TARGET_PAGE_BITS);
+    MemoryRegionSection *section;
+    subpage_t *subpage;
+
+    section = phys_page_find(as->dispatch, addr >> TARGET_PAGE_BITS);
+    if (resolve_subpage && section->mr->subpage) {
+        subpage = container_of(section->mr, subpage_t, iomem);
+        section = &phys_sections[subpage->sub_section[SUBPAGE_IDX(addr)]];
+    }
+    return section;
 }
 
-MemoryRegionSection *address_space_translate(AddressSpace *as, hwaddr addr,
-                                             hwaddr *xlat, hwaddr *plen,
-                                             bool is_write)
+static MemoryRegionSection *
+address_space_translate_internal(AddressSpace *as, hwaddr addr, hwaddr *xlat,
+                                 hwaddr *plen, bool resolve_subpage)
 {
     MemoryRegionSection *section;
     Int128 diff;
 
-    section = address_space_lookup_region(as, addr);
+    section = address_space_lookup_region(as, addr, resolve_subpage);
     /* Compute offset within MemoryRegionSection */
     addr -= section->offset_within_address_space;
 
@@ -243,6 +259,20 @@ MemoryRegionSection *address_space_translate(AddressSpace *as, hwaddr addr,
     *plen = int128_get64(int128_min(diff, int128_make64(*plen)));
     return section;
 }
+
+MemoryRegionSection *address_space_translate(AddressSpace *as, hwaddr addr,
+                                             hwaddr *xlat, hwaddr *plen,
+                                             bool is_write)
+{
+    return address_space_translate_internal(as, addr, xlat, plen, true);
+}
+
+MemoryRegionSection *
+address_space_translate_for_iotlb(AddressSpace *as, hwaddr addr, hwaddr *xlat,
+                                  hwaddr *plen)
+{
+    return address_space_translate_internal(as, addr, xlat, plen, false);
+}
 #endif
 
 void cpu_exec_init_all(void)
@@ -697,13 +727,6 @@ hwaddr memory_region_section_get_iotlb(CPUArchState *env,
 
 #if !defined(CONFIG_USER_ONLY)
 
-#define SUBPAGE_IDX(addr) ((addr) & ~TARGET_PAGE_MASK)
-typedef struct subpage_t {
-    MemoryRegion iomem;
-    hwaddr base;
-    uint16_t sub_section[TARGET_PAGE_SIZE];
-} subpage_t;
-
 static int subpage_register (subpage_t *mmio, uint32_t start, uint32_t end,
                              uint16_t section);
 static subpage_t *subpage_init(hwaddr base);
diff --git a/include/exec/cputlb.h b/include/exec/cputlb.h
index e821660..e21cb60 100644
--- a/include/exec/cputlb.h
+++ b/include/exec/cputlb.h
@@ -32,6 +32,10 @@ extern int tlb_flush_count;
 
 /* exec.c */
 void tb_flush_jmp_cache(CPUArchState *env, target_ulong addr);
+
+MemoryRegionSection *
+address_space_translate_for_iotlb(AddressSpace *as, hwaddr addr, hwaddr *xlat,
+                                  hwaddr *plen);
 hwaddr memory_region_section_get_iotlb(CPUArchState *env,
                                        MemoryRegionSection *section,
                                        target_ulong vaddr,
-- 
1.8.1.4