Re: [PATCH V2 1/1] target/loongarch: Fixed tlb huge page loading issue

[maobibo]

Sorry, manual is updated already and we do not notice that still.

https://www.loongson.cn/uploads/images/2023102309132647981.%E9%BE%99%E8%8A%AF%E6%9E%B6%E6%9E%84%E5%8F%82%E8%80%83%E6%89%8B%E5%86%8C%E5%8D%B7%E4%B8%80_r1p10.pdf

It is Chinese web link, English manual is not updated. Here is English 
translation by manual with instruction  "lddir rd, rj, level"

If the bit[14:13] of the register rj is not equal to 0 and its bit[6] 
is 1, the value of the register rj is a marked as HugePage page entries. 
In this case, the value from register rj is written directly to register rd.

If the bit[14:13] of the register rj is equal to 0 and its bit[6] is 1, 
the value of the register rj is an Hugepage table entry. In this case, 
replace the bit[14:13] of the register RJ value with level[1:0], the val 
is written to the register rd.

If the bit[6] bit of register rj is 0, the value of the universal 
register rj is the page table entry, it is  physical address base page 
table. In this case, if the LDDIR command is executed, the address will 
be refilled according to the TLB currently processed. Retrieve the base 
address of the next-level page table and write it to the common register 
rd.

We will remove temporary lddir_ps, and record page size with bit[14:13] 
in next version.

Regards
Bibo Mao

On 2024/3/6 下午12:10, Richard Henderson wrote:
> On 3/5/24 17:52, lixianglai wrote:
> > The LDDIR_PS variable is not described in detail in the manual, but is 
> > only an intermediate variable to assist in page size calculation 
> > during tcg simulation.
>
> This is exactly why I believe adding this intermediate variable is wrong.
>
> What happens if LDPTE is *not* preceded by LDDIR?  It's not the usual 
> way a tlb fill routine works, but *something* should happen if you 
> construct a valid huge page tlb entry by hand and pass it directly to 
> LDPTE.
>
> With your implementation, this will not work because lddir_ps will not 
> be initialized. But I expect that on real hardware it would work.
>
> If this does not work on real hardware, then there *is* some heretofore 
> undocumented hardware state.  If so, then we need a description of this 
> state from the hardware engineers -- the documentation of LDDIR and 
> LDPTE need updating.  Finally, this new hardware state needs to be added 
> to the migration state.
>
>
> r~