s390x/tcg: low-address protection support

This is a neat way to implement low address protection, whereby
only the first 512 bytes of the first two pages (each 4096 bytes) of
every address space are protected.

Store a tec of 0 for the access exception, this is what is defined by
Enhanced Suppression on Protection in case of a low address protection
(Bit 61 set to 0, rest undefined).

We have to make sure to to pass the access address, not the masked page
address into mmu_translate*().

Drop the check from testblock. So we can properly test this via
kvm-unit-tests.

This will check every access going through one of the MMUs.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20171016202358.3633-3-david@redhat.com>
[CH: restored error message for access register mode]
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

1 files changed, 0 insertions, 8 deletions

diff --git a/target/s390x/mem_helper.c b/target/s390x/mem_helper.c
index bbbe1c62b3..69a16867d4 100644
--- a/target/s390x/mem_helper.c
+++ b/target/s390x/mem_helper.c
@@ -1687,18 +1687,10 @@ void HELPER(stctl)(CPUS390XState *env, uint32_t r1, uint64_t a2, uint32_t r3)
 uint32_t HELPER(testblock)(CPUS390XState *env, uint64_t real_addr)
 {
     uintptr_t ra = GETPC();
-    CPUState *cs = CPU(s390_env_get_cpu(env));
     int i;
 
     real_addr = wrap_address(env, real_addr) & TARGET_PAGE_MASK;
 
-    /* Check low-address protection */
-    if ((env->cregs[0] & CR0_LOWPROT) && real_addr < 0x2000) {
-        cpu_restore_state(cs, ra);
-        program_interrupt(env, PGM_PROTECTION, 4);
-        return 1;
-    }
-
     for (i = 0; i < TARGET_PAGE_SIZE; i += 8) {
         cpu_stq_real_ra(env, real_addr + i, 0, ra);
     }