On 9/13/23 18:55, Richard Henderson wrote:
On 9/13/23 07:47, Helge Deller wrote:
+ haddr = (uint32_t *)((uintptr_t)vaddr);
+ old = *haddr;
This is horribly incorrect, both for user-only and system mode.
Richard, thank you for the review!
But would you mind explaining why this is incorrect?
I thought the "vaddr = probe_access()" calculates the host address, so
shouldn't it be the right address?
+ /* if already zero, do not write 0 again to reduce memory presssure */
+ if (old == 0) {
+ return 0;
+ }
+ old = qatomic_xchg(haddr, (uint32_t) 0);
You're also dropping the required host memory barrier.
?
Frankly, the current tcg_gen_atomic_xchg_reg is as optimized as you'll be able to do. I
really doubt the "avoid write 0" is measurable at all.
Helge
