Re: [PATCH v3 6/6] x86, mm: Support huge KVA mappings on x86

[Toshi Kani]

On Tue, 2015-03-03 at 14:44 -0800, Andrew Morton wrote:
> On Tue,  3 Mar 2015 10:44:24 -0700 Toshi Kani <toshi.kani@xxxxxx> wrote:
 :
> > +
> > +#ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
> > +int pud_set_huge(pud_t *pud, phys_addr_t addr, pgprot_t prot)
> > +{
> > +	u8 mtrr;
> > +
> > +	/*
> > +	 * Do not use a huge page when the range is covered by non-WB type
> > +	 * of MTRRs.
> > +	 */
> > +	mtrr = mtrr_type_lookup(addr, addr + PUD_SIZE);
> > +	if ((mtrr != MTRR_TYPE_WRBACK) && (mtrr != 0xFF))
> > +		return 0;
> 
> It would be good to notify the operator in some way when this happens. 
> Otherwise the kernel will run more slowly and there's no way of knowing
> why.  I guess slap a pr_info() in there.  Or maybe pr_warn()?

We only use 4KB mappings today, so this case will not make it run
slowly, i.e. it will be the same as today.  Also, adding a message here
can generate a lot of messages when MTRRs cover a large area.  So, I
think we are fine without a message.

> 
> > +	prot = pgprot_4k_2_large(prot);
> > +
> > +	set_pte((pte_t *)pud, pfn_pte(
> > +		(u64)addr >> PAGE_SHIFT,
> > +		__pgprot(pgprot_val(prot) | _PAGE_PSE)));
> > +
> > +	return 1;
> > +}
> > +
> > +int pmd_set_huge(pmd_t *pmd, phys_addr_t addr, pgprot_t prot)
> > +{
> > +	u8 mtrr;
> > +
> > +	/*
> > +	 * Do not use a huge page when the range is covered by non-WB type
> > +	 * of MTRRs.
> > +	 */
> > +	mtrr = mtrr_type_lookup(addr, addr + PMD_SIZE);
> > +	if ((mtrr != MTRR_TYPE_WRBACK) && (mtrr != 0xFF))
> > +		return 0;
> > +
> > +	prot = pgprot_4k_2_large(prot);
> > +
> > +	set_pte((pte_t *)pmd, pfn_pte(
> > +		(u64)addr >> PAGE_SHIFT,
> > +		__pgprot(pgprot_val(prot) | _PAGE_PSE)));
> > +
> > +	return 1;
> > +}
> >
> > +int pud_clear_huge(pud_t *pud)
> > +{
> > +	if (pud_large(*pud)) {
> > +		pud_clear(pud);
> > +		return 1;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +int pmd_clear_huge(pmd_t *pmd)
> > +{
> > +	if (pmd_large(*pmd)) {
> > +		pmd_clear(pmd);
> > +		return 1;
> > +	}
> > +
> > +	return 0;
> > +}
> 
> I didn't see anywhere where the return values of these functions are
> documented.  It's all fairly obvious, but we could help the rearers
> a bit.

Agreed.  I will add function headers with descriptions to the new
functions.

Thanks,
-Toshi 


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