Re: [PATCH 1/1] RDMA/rxe: Fix blktests srp lead kernel panic with 64k page size

[Zhu Yanjun <yanjun.zhu@linux.dev>]

在 2023/10/27 7:23, Jason Gunthorpe 写道:
> On Thu, Oct 26, 2023 at 08:59:34PM +0800, Zhu Yanjun wrote:
>> 在 2023/10/26 19:42, Jason Gunthorpe 写道:
>>> On Thu, Oct 26, 2023 at 09:05:52AM +0000, Zhijian Li (Fujitsu) wrote:
>>>> The root cause is that
>>>>
>>>> rxe:rxe_set_page() gets wrong when mr.page_size != PAGE_SIZE where it only stores the *page to xarray.
>>>> So the offset will get lost.
>>>>
>>>> For example,
>>>> store process:
>>>> page_size = 0x1000;
>>>> PAGE_SIZE = 0x10000;
>>>> va0 = 0xffff000020651000;
>>>> page_offset = 0 = va & (page_size - 1);
>>>> page = va_to_page(va);
>>>> xa_store(&mr->page_list, mr->nbuf, page, GFP_KERNEL);
>>>>
>>>> load_process:
>>>> page = xa_load(&mr->page_list, index);
>>>> page_va = kmap_local_page(page) --> it must be a PAGE_SIZE align value, assume it as 0xffff000020650000
>>>> va1 = page_va + page_offset = 0xffff000020650000 + 0 = 0xffff000020650000;
>>>>
>>>> Obviously, *va0 != va1*, page_offset get lost.
>>>>
>>>>
>>>> How to fix:
>>>> - revert 325a7eb85199 ("RDMA/rxe: Cleanup page variables in rxe_mr.c")
>>>> - don't allow ulp registering mr.page_size != PAGE_SIZE ?
>>> Lets do the second one please. Most devices only support PAGE_SIZE anyhow.
>> Normally page_size is PAGE_SIZE or the size of the whole compound page (in
>> the latest kernel version, it is the size of folio). When compound page or
>> folio is taken into account, the page_size is not equal to
>> PAGE_SIZE.
> folios are always multiples of PAGE_SIZE. rxe splits everything into
> PAGE_SIZE units in the xarray.
>
>> If the ULP uses the compound page or folio, the similar problem will occur
>> again.
> No, it won't. We never store folios in the xarray.

Sure.

I mean, in ULP, if folio is used, the page size is set to multiple 
PAGE_SIZE, but in RXE, the page size is set to PAGE_SIZE.

So the page size in ULP is different with the page size in RXE.

I am not sure whether this similar problem still occur or not.

I hope this problem will not occur even with folio.

Zhu Yanjun

>
> Jason