target/arm/hvf: sign extend the data for a load operation when SSE=1

In the syndrome value for a data abort, bit 21 is SSE, which is
set to indicate that the abort was on a sign-extending load. When
we handle the data abort from the guest via address_space_read(),
we forgot to handle this and so would return the wrong value if
the guest did a sign-extending load to an MMIO region. Add the
sign-extension of the returned data.

Cc: qemu-stable@nongnu.org
Signed-off-by: Joelle van Dyne <j@getutm.app>
Message-id: 20250224184123.50780-1-j@getutm.app
[PMM: Drop an unnecessary check on 'len'; expand commit message]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Author: Joelle van Dyne

target/arm/hvf/hvf.c

@@ -1983,6 +1983,7 @@ int hvf_vcpu_exec(CPUState *cpu)
         bool isv = syndrome & ARM_EL_ISV;
         bool iswrite = (syndrome >> 6) & 1;
         bool s1ptw = (syndrome >> 7) & 1;
+        bool sse = (syndrome >> 21) & 1;
         uint32_t sas = (syndrome >> 22) & 3;
         uint32_t len = 1 << sas;
         uint32_t srt = (syndrome >> 16) & 0x1f;
@@ -2010,6 +2011,9 @@ int hvf_vcpu_exec(CPUState *cpu)
             address_space_read(&address_space_memory,
                                hvf_exit->exception.physical_address,
                                MEMTXATTRS_UNSPECIFIED, &val, len);
+            if (sse) {
+                val = sextract64(val, 0, len * 8);
+            }
             hvf_set_reg(cpu, srt, val);
         }