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accel/tcg: Perform aligned atomic reads in translator_ld

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Perform aligned atomic reads in translator_ld, if possible.
According to

https://lore.kernel.org/qemu-devel/20240607101403.1109-1-jim.shu@sifive.com/

this is required for RISC-V Ziccif.

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2025-03-11 18:34:58 -07:00
parent 4ba597c138
commit 6a9dfe1984
1 changed files with 38 additions and 4 deletions
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42
accel/tcg/translator.c
View file

@ -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;
}