linux-kernel - Re: [patch V3 13/37] mips/mm/highmem: Switch to generic kmap atomic

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Message-Id: <DUUPMQ.U53A0W7YJPGM@crapouillou.net>
Date:   Sun, 10 Jan 2021 11:35:01 +0000
From:   Paul Cercueil <paul@...pouillou.net>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
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Subject: Re: [patch V3 13/37] mips/mm/highmem: Switch to generic kmap atomic

Hi Thomas,

Le sam. 9 janv. 2021 à 1:33, Thomas Bogendoerfer 
<tsbogend@...ha.franken.de> a écrit :
> On Sat, Jan 09, 2021 at 12:58:05AM +0100, Thomas Bogendoerfer wrote:
>>  On Fri, Jan 08, 2021 at 08:20:43PM +0000, Paul Cercueil wrote:
>>  > Hi Thomas,
>>  >
>>  > 5.11 does not boot anymore on Ingenic SoCs, I bisected it to this 
>> commit.
>>  >
>>  > Any idea what could be happening?
>> 
>>  not yet, kernel crash log of a Malta QEMU is below.
> 
> update:
> 
> This dirty hack lets the Malta QEMU boot again:
> 
> diff --git a/mm/highmem.c b/mm/highmem.c
> index c3a9ea7875ef..190cdda1149d 100644
> --- a/mm/highmem.c
> +++ b/mm/highmem.c
> @@ -515,7 +515,7 @@ void *__kmap_local_pfn_prot(unsigned long pfn, 
> pgprot_t prot)
>  	vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
>  	BUG_ON(!pte_none(*(kmap_pte - idx)));
>  	pteval = pfn_pte(pfn, prot);
> -	set_pte_at(&init_mm, vaddr, kmap_pte - idx, pteval);
> +	set_pte(kmap_pte - idx, pteval);
>  	arch_kmap_local_post_map(vaddr, pteval);
>  	current->kmap_ctrl.pteval[kmap_local_idx()] = pteval;
>  	preempt_enable();
> 
> set_pte_at() tries to update cache and could do an kmap_atomic() 
> there.
> Not sure, if this is allowed at this point.

Yes, I can confirm that your workaround works here too.

Cheers,
-Paul