On 17/03/16 18:14, Sergey Fedorov wrote:
> On 17/03/16 18:09, Paolo Bonzini wrote:
>>
>> On 17/03/2016 14:46, sergey.fedo...@linaro.org wrote:
>>> void tb_phys_invalidate(TranslationBlock *tb, tb_page_addr_t
>>> page_addr)
>>> {
>>> - CPUState *cpu;
>>> PageDesc *p;
>>> unsigned int h, n1;
>>> + tb_page_addr_t pc;
>>> tb_page_addr_t phys_pc;
>>> TranslationBlock *tb1, *tb2;
>>> - /* remove the TB from the hash list */
>>> - phys_pc = tb->page_addr[0] + (tb->pc & ~TARGET_PAGE_MASK);
>>> - h = tb_phys_hash_func(phys_pc);
>>> - tb_hash_remove(&tcg_ctx.tb_ctx.tb_phys_hash[h], tb);
>>> -
>>> - /* remove the TB from the page list */
>>> - if (tb->page_addr[0] != page_addr) {
>>> - p = page_find(tb->page_addr[0] >> TARGET_PAGE_BITS);
>>> - tb_page_remove(&p->first_tb, tb);
>>> - invalidate_page_bitmap(p);
>>> - }
>>> - if (tb->page_addr[1] != -1 && tb->page_addr[1] != page_addr) {
>>> - p = page_find(tb->page_addr[1] >> TARGET_PAGE_BITS);
>>> - tb_page_remove(&p->first_tb, tb);
>>> - invalidate_page_bitmap(p);
>>> - }
>>> -
>>> - tcg_ctx.tb_ctx.tb_invalidated_flag = 1;
>>> -
>> Did you investigate the removal of this setting of tb_invalidated_flag?
>>
>> My recollection is that it is okay to remove it because at worse it
>> would cause a tb_add_jump from an invalidated source to a valid
>> destination. This should be harmless as long as the source has been
>> tb_phys_invalidated and not tb_flushed. But this needs to be checked.
>
> Thanks for pointing that. I should investigate it to make sure,
> although arm32/arm64/x86_64 Linux boots fine as well as the latest
> Alex's kmv-unit-tests pass.
The use pattern of 'tb_invalidated_flag' is a bit intricate; correct me,
if I'm wrong about the following. Basically, 'tb_invalidated_flag' was
meant to catch two events:
* some TB has been invalidated by tb_phys_invalidate();
* the whole translation buffer has been flushed by tb_flush().
Then it is checked to ensure:
* the last executed TB can be safely patched to directly call the next
one in cpu_exec();
* the original TB should be provided for further possible invalidation
along with the temporarily generated TB when in cpu_exec_nocache().
What, I think, we couldn't be sure in is the cpu_exec_nocache() case. It
could look like a kind of corner case, but it could result in stalls, if
the original TB isn't invalidated properly, see b4ac20b4df0d ("cpu-exec:
fix cpu_exec_nocache").
So I would suggest the following solution:s
(1) Use 'tb->pc' as an indicator of whether TB is valid; check for it
in cpu_exec() when deciding on whether to patch the last executed
TB or not
(2) Use 'tcg_ctx.tb_ctx.tb_flush_count' to check for translation buffer
flushes; capture it before calling tb_gen_code() and compare to it
afterwards to check if tb_flush() has been called in between
What do you think?
Kind regards,
Sergey
