On Wed, Mar 19, 2025 at 7:36 AM Richard Henderson
<richard.hender...@linaro.org> wrote:
>
> Perform aligned atomic reads in translator_ld, if possible.
> According to
>
> https://lore.kernel.org/qemu-devel/20240607101403.1109-1-jim....@sifive.com/
>
> this is required for RISC-V Ziccif.
Thanks Richard!!
>
> Signed-off-by: Richard Henderson <richard.hender...@linaro.org>
Reviewed-by: Alistair Francis <alistair.fran...@wdc.com>
Alistair
> ---
> accel/tcg/translator.c | 42 ++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 38 insertions(+), 4 deletions(-)
>
> diff --git a/accel/tcg/translator.c b/accel/tcg/translator.c
> index ef1538b4fc..157be33bf6 100644
> --- a/accel/tcg/translator.c
> +++ b/accel/tcg/translator.c
> @@ -265,12 +265,14 @@ static bool translator_ld(CPUArchState *env,
> DisasContextBase *db,
>
> if (likely(((base ^ last) & TARGET_PAGE_MASK) == 0)) {
> /* Entire read is from the first page. */
> - memcpy(dest, host + (pc - base), len);
> - return true;
> + goto do_read;
> }
>
> if (unlikely(((base ^ pc) & TARGET_PAGE_MASK) == 0)) {
> - /* Read begins on the first page and extends to the second. */
> + /*
> + * Read begins on the first page and extends to the second.
> + * The unaligned read is never atomic.
> + */
> size_t len0 = -(pc | TARGET_PAGE_MASK);
> memcpy(dest, host + (pc - base), len0);
> pc += len0;
> @@ -329,7 +331,39 @@ static bool translator_ld(CPUArchState *env,
> DisasContextBase *db,
> host = db->host_addr[1];
> }
>
> - memcpy(dest, host + (pc - base), len);
> + do_read:
> + /*
> + * Assume aligned reads should be atomic, if possible.
> + * We're not in a position to jump out with EXCP_ATOMIC.
> + */
> + host += pc - base;
> + switch (len) {
> + case 2:
> + if (QEMU_IS_ALIGNED(pc, 2)) {
> + uint16_t t = qatomic_read((uint16_t *)host);
> + stw_he_p(dest, t);
> + return true;
> + }
> + break;
> + case 4:
> + if (QEMU_IS_ALIGNED(pc, 4)) {
> + uint32_t t = qatomic_read((uint32_t *)host);
> + stl_he_p(dest, t);
> + return true;
> + }
> + break;
> +#ifdef CONFIG_ATOMIC64
> + case 8:
> + if (QEMU_IS_ALIGNED(pc, 8)) {
> + uint64_t t = qatomic_read__nocheck((uint64_t *)host);
> + stq_he_p(dest, t);
> + return true;
> + }
> + break;
> +#endif
> + }
> + /* Unaligned or partial read from the second page is not atomic. */
> + memcpy(dest, host, len);
> return true;
> }
>
> --
> 2.43.0
>
>
