Re: [Qemu-devel] [PATCH 01/26] tcg: Assert h2g_valid for 32-bit guest on 64-bit host

[Peter Maydell]

On Wed, 3 Apr 2019 at 10:46, Richard Henderson
<address@hidden> wrote:
>
> For this combination, we can tell whether or not the address
> being accessed is within the 4GB range that is accessible by
> the guest.  Otherwise the fault must be elsewhere in qemu,
> accessing qemu data structures.
>
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>  accel/tcg/user-exec.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/accel/tcg/user-exec.c b/accel/tcg/user-exec.c
> index 0789984fe6..fa9380a380 100644
> --- a/accel/tcg/user-exec.c
> +++ b/accel/tcg/user-exec.c
> @@ -143,6 +143,15 @@ static inline int handle_cpu_signal(uintptr_t pc, 
> siginfo_t *info,
>          }
>      }
>
> +    /*
> +     * For a 32-bit guest on a 64-bit host, the set of addresses that we
> +     * access on behalf of the guest is constrained.  Anything outside
> +     * that range is a bug elsewhere in QEMU.
> +     */
> +#if TARGET_LONG_BITS == 32 && HOST_LONG_BITS == 64
> +    g_assert(h2g_valid(address));
> +#endif

I'm not sure this is right. h2g_valid() will check whether the guest address is
below GUEST_ADDR_MAX. For architectures which set
TARGET_VIRT_ADDR_SPACE_BITS to something less than 32 there are
address values which aren't h2g_valid() but which we still want to cause
a guest exception rather than asserting, aren't there ?

thanks
-- PMM