On 3/18/25 14:31, Richard Henderson 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.
Signed-off-by: Richard Henderson <richard.hender...@linaro.org>
---
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;
}
Reviewed-by: Pierrick Bouvier <pierrick.bouv...@linaro.org>
