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

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Date:   Sun, 10 Jan 2021 12:53:10 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
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Subject: Re: [patch V3 13/37] mips/mm/highmem: Switch to generic kmap atomic


> Am 10.01.2021 um 12:35 schrieb Paul Cercueil <paul@...pouillou.net>:
> 
> 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.

Just for completeness, I have no such problems booting CI20/jz4780 or Skytone400/jz4730 (unpublished work) with 5.11-rc2.
But may depend on board capabilites (ram size, memory layout or something else).

>>> >
>>> > 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
> 
>