Re: [PATCH 1/1] accel/tcg: Allow the second page of an instruction to be MMIO

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 6/2/23 20:38, Richard Henderson wrote:
> If an instruction straddles a page boundary, and the first page
> was ram, but the second page was MMIO, we would abort.  Handle
> this as if both pages are MMIO, by setting the ram_addr_t for
> the first page to -1.
> 
> Reported-by: Sid Manning <sidneym@quicinc.com>
> Reported-by: Jørgen Hansen <Jorgen.Hansen@wdc.com>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   accel/tcg/translator.c | 12 ++++++++++--
>   1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/accel/tcg/translator.c b/accel/tcg/translator.c
> index ef5193c67e..1cf404ced0 100644
> --- a/accel/tcg/translator.c
> +++ b/accel/tcg/translator.c
> @@ -176,8 +176,16 @@ static void *translator_access(CPUArchState *env, DisasContextBase *db,
>           if (host == NULL) {
>               tb_page_addr_t phys_page =
>                   get_page_addr_code_hostp(env, base, &db->host_addr[1]);
> -            /* We cannot handle MMIO as second page. */
> -            assert(phys_page != -1);
> +
> +            /*
> +             * If the second page is MMIO, treat as if the first page
> +             * was MMIO as well, so that we do not cache the TB.
> +             */
> +            if (unlikely(phys_page == -1)) {
> +                tb_set_page_addr0(tb, -1);

Nice trick! I'm tempted to log it at CPU_LOG_EXEC (or
CPU_LOG_TB_CPU) level.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

> +                return NULL;
> +            }
> +
>               tb_set_page_addr1(tb, phys_page);
>   #ifdef CONFIG_USER_ONLY
>               page_protect(end);