linux-kernel - Re: [PATCH 02/11] mm: ioremap: fixup the physical address

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Date:   Sun, 7 Aug 2022 10:11:05 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Alexander Gordeev <agordeev@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, hch@...radead.org,
        wangkefeng.wang@...wei.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 02/11] mm: ioremap: fixup the physical address

On 08/04/22 at 06:02pm, Alexander Gordeev wrote:
> On Mon, Aug 01, 2022 at 10:40:20PM +0800, Baoquan He wrote:
> > This is a preparation patch, no functionality change.
> 
> There is, please see below.
> 
> > @@ -3,11 +3,17 @@
> >  #include <linux/mm.h>
> >  #include <linux/io.h>
> >  
> > -void __iomem *ioremap_allowed(phys_addr_t phys_addr, size_t size, unsigned long prot)
> > +void __iomem *
> > +ioremap_allowed(phys_addr_t *paddr, size_t size, unsigned long *prot_val)
> >  {
> > -	unsigned long last_addr = phys_addr + size - 1;
> > +	unsigned long last_addr, offset, phys_addr = *paddr;
> >  	int ret = -EINVAL;
> >  
> > +	offset = phys_addr & (~PAGE_MASK);
> > +	phys_addr -= offset;
> 
> FWIW, phys_addr &= PAGE_MASK looks much more usual.

Sure, will change.

> 
> > @@ -11,13 +11,20 @@
> >  #include <linux/io.h>
> >  #include <linux/export.h>
> >  
> > -void __iomem *ioremap_prot(phys_addr_t phys_addr, size_t size,
> > +void __iomem *ioremap_prot(phys_addr_t paddr, size_t size,
> >  			   unsigned long prot)
> >  {
> >  	unsigned long offset, vaddr;
> > -	phys_addr_t last_addr;
> > +	phys_addr_t last_addr, phys_addr = paddr;
> >  	struct vm_struct *area;
> >  	void __iomem *base;
> > +	unsigned long prot_val = prot;
> 
> Why prot_val is needed?

I will remove it and pass &prot to ioremap_allowed(). I could think too
much when I made change here. Thanks.

> 
> > +	base = ioremap_allowed(&phys_addr, size, &prot_val);
> > +	if (IS_ERR(base))
> > +		return NULL;
> > +	else if (base)
> > +		return base;
> 
> By moving ioremap_allowed() here you allow it to be called
> before the wrap-around check, including architectures that
> do not do fixups.

Yes, just as you say.

> 
> And now ioremap_allowed() semantics, prototype and name turn
> less than obvious. Why not introduce a separate fixup callback?

I can do that, while a little worried if too many hooks introduced.
I will introduce another fixup hook in v2 if no other suggestion or
concern. Thanks.


> 
> >  	/* Disallow wrap-around or zero size */
> >  	last_addr = phys_addr + size - 1;
> > @@ -29,12 +36,6 @@ void __iomem *ioremap_prot(phys_addr_t phys_addr, size_t size,
> >  	phys_addr -= offset;
> >  	size = PAGE_ALIGN(size + offset);
> >  
> > -	base = ioremap_allowed(phys_addr, size, prot);
> > -	if (IS_ERR(base))
> > -		return NULL;
> > -	else if (base)
> > -		return base;
> > -
> >  	area = get_vm_area_caller(size, VM_IOREMAP,
> >  			__builtin_return_address(0));
> >  	if (!area)
>