[Qemu-devel] [PATCH v1 2/4] s390x/tcg: Introduce probe_read_access()

[David Hildenbrand <david@redhat.com>]

Let's introduce a helper to probe read access (by actually reading a
piece of data of every page) and add a comment why this might not be
100% safe in all scenarios. Once we actually run into that issue, we'll
have to think of something else.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 target/s390x/internal.h   |  2 ++
 target/s390x/mem_helper.c | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/target/s390x/internal.h b/target/s390x/internal.h
index c243fa725b..bdb833c525 100644
--- a/target/s390x/internal.h
+++ b/target/s390x/internal.h
@@ -354,6 +354,8 @@ void ioinst_handle_sal(S390CPU *cpu, uint64_t reg1, uintptr_t ra);
 
 /* mem_helper.c */
 target_ulong mmu_real2abs(CPUS390XState *env, target_ulong raddr);
+void probe_read_access(CPUS390XState *env, uint64_t addr, uint64_t len,
+                       uintptr_t ra);
 void probe_write_access(CPUS390XState *env, uint64_t addr, uint64_t len,
                         uintptr_t ra);
 
diff --git a/target/s390x/mem_helper.c b/target/s390x/mem_helper.c
index 7819aca15d..4e9d126e2c 100644
--- a/target/s390x/mem_helper.c
+++ b/target/s390x/mem_helper.c
@@ -2612,6 +2612,40 @@ uint32_t HELPER(cu42)(CPUS390XState *env, uint32_t r1, uint32_t r2, uint32_t m3)
                            decode_utf32, encode_utf16);
 }
 
+/*
+ * Make sure the read access is permitted and TLB entries are created. In
+ * very rare cases it might happen that the actual accesses might need
+ * new MMU translations. If the page tables were changed in between, we
+ * might still trigger a fault. However, this seems to barely happen, so we
+ * can ignore this for now.
+ */
+void probe_read_access(CPUS390XState *env, uint64_t addr, uint64_t len,
+                       uintptr_t ra)
+{
+#ifdef CONFIG_USER_ONLY
+    if (!guest_addr_valid(addr) || !guest_addr_valid(addr + len - 1) ||
+        page_check_range(addr, len, PAGE_READ) < 0) {
+        s390_program_interrupt(env, PGM_ADDRESSING, ILEN_AUTO, ra);
+    }
+#else
+    while (len) {
+        const uint64_t pagelen = -(addr | -TARGET_PAGE_MASK);
+        const uint64_t curlen = MIN(pagelen, len);
+
+        cpu_ldub_data_ra(env, addr, ra);
+        addr = wrap_address(env, addr + curlen);
+        len -= curlen;
+    }
+#endif
+}
+
+/*
+ * Make sure the write access is permitted and TLB entries are created. In
+ * very rare cases it might happen that the actual accesses might need
+ * new MMU translations - especially, on LAP protected pages. If the page
+ * tables were changed in between, we might still trigger a fault. However,
+ * this seems to barely happen, so we can ignore this for now.
+ */
 void probe_write_access(CPUS390XState *env, uint64_t addr, uint64_t len,
                         uintptr_t ra)
 {
-- 
2.21.0