linux-kernel - Re: [PATCH] ARC: Use 40-bit physical page mask for PAE

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Date:   Mon, 26 Apr 2021 17:16:01 +0000
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     Vladimir Isaev <Vladimir.Isaev@...opsys.com>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>
CC:     "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "rppt@...ux.ibm.com" <rppt@...ux.ibm.com>,
        Arnd Bergmann <arnd@...nel.org>
Subject: Re: [PATCH] ARC: Use 40-bit physical page mask for PAE

On 4/26/21 9:43 AM, Vladimir Isaev wrote:
> Hi,
>
> On Monday, April 26, 2021 7:30 PM, Vineet Gupta wrote:
>> On 4/26/21 3:08 AM, Vladimir Isaev wrote:
>>
>>>    #endif /* _UAPI__ASM_ARC_PAGE_H */
>>> diff --git a/arch/arc/mm/ioremap.c b/arch/arc/mm/ioremap.c
>>> index fac4adc90204..eb109d57d544 100644
>>> --- a/arch/arc/mm/ioremap.c
>>> +++ b/arch/arc/mm/ioremap.c
>>> @@ -71,8 +71,8 @@ void __iomem *ioremap_prot(phys_addr_t paddr,
>> unsigned long size,
>>>    	prot = pgprot_noncached(prot);
>>>
>>>    	/* Mappings have to be page-aligned */
>>> -	off = paddr & ~PAGE_MASK;
>> This is offset *within* a page so upper bits must not matter. In fact,
>> with this a bogus offset like 0xFF_FFFFFFFF can turn into something
>> weird such as 0xFF_00000000
> I understand, but idea here is to use PHYSICAL_PAGE_MASK/PAGE_MASK_PHYS
> for any phys_addr_t variable without thinking. So if off is actually offset for
> virtual address we can use unsigned long for it.

@off here is for a physical address, but is it intra-page still so 
doesn't matter if virtual or phy. Indeed it is a good idea to fix it to 
be unsigned int (not long since that is 64-bit attuned)

-Vineet