From: Remi Denis-Courmont <remi.denis.courmont@huawei.com>

Since QEMU does not support the ARMv8.2-LVA, Large Virtual Address,
extension (yet), the VA address space is 48-bits plus a sign bit. User
mode can only handle the positive half of the address space, so that
makes a limit of 48 bits.

(With LVA, it would be 53 and 52 bits respectively.)

The incorrectly large address space conflicts with PAuth instructions,
which bits 48-54 and 56-63 for the pointer authentication code. This
also conflicts with (as yet unsupported by QEMU) data tagging and with
the ARMv8.5-MTE extension.

Signed-off-by: Remi Denis-Courmont <remi.denis.courmont@huawei.com>
---
 target/arm/cpu.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index ff81db420d..a3781600ba 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -2503,7 +2503,7 @@ bool write_cpustate_to_list(ARMCPU *cpu);
 
 #if defined(TARGET_AARCH64)
 #  define TARGET_PHYS_ADDR_SPACE_BITS 48
-#  define TARGET_VIRT_ADDR_SPACE_BITS 64
+#  define TARGET_VIRT_ADDR_SPACE_BITS 48
 #else
 #  define TARGET_PHYS_ADDR_SPACE_BITS 40
 #  define TARGET_VIRT_ADDR_SPACE_BITS 32
-- 
2.20.1

On 1/25/19 10:52 PM, Rémi Denis-Courmont wrote:
> From: Remi Denis-Courmont <remi.denis.courmont@huawei.com>
> 
> Since QEMU does not support the ARMv8.2-LVA, Large Virtual Address,
> extension (yet), the VA address space is 48-bits plus a sign bit. User
> mode can only handle the positive half of the address space, so that
> makes a limit of 48 bits.
> 
> (With LVA, it would be 53 and 52 bits respectively.)
> 
> The incorrectly large address space conflicts with PAuth instructions,
> which bits 48-54 and 56-63 for the pointer authentication code. This
> also conflicts with (as yet unsupported by QEMU) data tagging and with
> the ARMv8.5-MTE extension.
> 
> Signed-off-by: Remi Denis-Courmont <remi.denis.courmont@huawei.com>
> ---
>  target/arm/cpu.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~