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

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Message-ID: <BY5PR12MB4131E059EA9C630661349A0EDF429@BY5PR12MB4131.namprd12.prod.outlook.com>
Date:   Mon, 26 Apr 2021 16:43:22 +0000
From:   Vladimir Isaev <Vladimir.Isaev@...opsys.com>
To:     Vineet Gupta <Vineet.Gupta1@...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

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.

Thank you,
Vladimir Isaev