netdev - RE: [PATCH v2 01/12] x86/ioremap: Fix page aligned size calculation in __ioremap

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Date:   Mon, 14 Nov 2022 16:53:36 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        "hpa@...or.com" <hpa@...or.com>, KY Srinivasan <kys@...rosoft.com>,
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Subject: RE: [PATCH v2 01/12] x86/ioremap: Fix page aligned size calculation
 in __ioremap_caller()

From: Dave Hansen <dave.hansen@...el.com> Sent: Monday, November 14, 2022 8:40 AM
> 
> On 11/10/22 22:21, Michael Kelley wrote:
> > --- a/arch/x86/mm/ioremap.c
> > +++ b/arch/x86/mm/ioremap.c
> > @@ -218,7 +218,7 @@ static void __ioremap_check_mem(resource_size_t addr,
> unsigned long size,
> >  	 */
> >  	offset = phys_addr & ~PAGE_MASK;
> >  	phys_addr &= PHYSICAL_PAGE_MASK;
> > -	size = PAGE_ALIGN(last_addr+1) - phys_addr;
> > +	size = (PAGE_ALIGN(last_addr+1) & PHYSICAL_PAGE_MASK) - phys_addr;
> 
> Michael, thanks for the explanation in your other reply.  First and
> foremost, I *totally* missed the reason for this patch.  I was thinking
> about issues that could pop up from the _lower_ bits being masked off.
> 
> Granted, your changelog _did_ say "upper bits", so shame on me.  But, it
> would be great to put some more background in the changelog to make it a
> bit harder for silly reviewers to miss such things.
> 
> I'd also like to propose something that I think is more straightforward:
> 
>         /*
>          * Mappings have to be page-aligned
>          */
>         offset = phys_addr & ~PAGE_MASK;
>         phys_addr &= PAGE_MASK;
>         size = PAGE_ALIGN(last_addr+1) - phys_addr;
> 
> 	/*
> 	 * Mask out any bits not parts of the actual physical
> 	 * address, like memory encryption bits.
> 	 */
> 	phys_addr &= PHYSICAL_PAGE_MASK;
> 
> Because, first of all, that "Mappings have to be page-aligned" thing is
> (now) doing more than page-aligning things.  Second, the moment you mask
> out the metadata bits, the 'size' calculation gets harder.  Doing it in
> two phases (page alignment followed by metadata bit masking) breaks up
> the two logical operations.
> 

Work for me.  Will do this in v3.

Michael