[PATCH v11] mm,kfence: decouple kfence from page granularity mapping judgement

[Zhenhua Huang]

On 2023/3/17 5:43, Marco Elver wrote:
> On Thu, 16 Mar 2023 at 16:10, Zhenhua Huang <quic_zhenhuah at quicinc.com> wrote:
>>
>> Kfence only needs its pool to be mapped as page granularity, if it is
>> inited early. Previous judgement was a bit over protected. From [1], Mark
>> suggested to "just map the KFENCE region a page granularity". So I
>> decouple it from judgement and do page granularity mapping for kfence
>> pool only. Need to be noticed that late init of kfence pool still requires
>> page granularity mapping.
>>
>> Page granularity mapping in theory cost more(2M per 1GB) memory on arm64
>> platform. Like what I've tested on QEMU(emulated 1GB RAM) with
>> gki_defconfig, also turning off rodata protection:
>> Before:
>> [root at liebao ]# cat /proc/meminfo
>> MemTotal:         999484 kB
>> After:
>> [root at liebao ]# cat /proc/meminfo
>> MemTotal:        1001480 kB
>>
>> To implement this, also relocate the kfence pool allocation before the
>> linear mapping setting up, arm64_kfence_alloc_pool is to allocate phys
>> addr, __kfence_pool is to be set after linear mapping set up.
>>
>> LINK: [1] https://lore.kernel.org/linux-arm-kernel/Y+IsdrvDNILA59UN@FVFF77S0Q05N/
>> Suggested-by: Mark Rutland <mark.rutland at arm.com>
>> Signed-off-by: Zhenhua Huang <quic_zhenhuah at quicinc.com>
>> Reviewed-by: Kefeng Wang <wangkefeng.wang at huawei.com>
> 
> Reviewed-by: Marco Elver <elver at google.com>
> 
> One question: what happens if the page-granular direct map is
> requested either way, is there any downside with this patch? Does it
> mean map_mem() just does a little extra work it shouldn't have? (Not
> saying that's a problem, just trying to ask you to double-check it's
> ok.)
> 

Yeah.. I think so Marco. Seems the extra work in map_mem() is we did 
judgement there.. Other side is we added one early param.

> However, please also wait for an arm64 maintainer to have a look. I'm
> assuming that because it touches mostly arm64 code, this patch ought
> to go through the arm64 tree?

Yeah, sure. We will wait for arm64 maintainers' comments.

Thanks,
Zhenhua

> 
> Thanks,
> -- Marco