Re: [PATCH v2 2/4] ioremap: Implement TLB_INV before huge mapping

[Chintan Pandya]

On 3/15/2018 7:01 PM, Mark Rutland wrote:
> On Thu, Mar 15, 2018 at 06:15:04PM +0530, Chintan Pandya wrote:
> > @@ -91,10 +93,15 @@ static inline int ioremap_pmd_range(pud_t *pud, unsigned long addr,
> >   
> >   		if (ioremap_pmd_enabled() &&
> >   		    ((next - addr) == PMD_SIZE) &&
> > -		    IS_ALIGNED(phys_addr + addr, PMD_SIZE) &&
> > -		    pmd_free_pte_page(pmd)) {
> > -			if (pmd_set_huge(pmd, phys_addr + addr, prot))
> > +		    IS_ALIGNED(phys_addr + addr, PMD_SIZE)) {
> > +			old_pmd = *pmd;
> > +			pmd_clear(pmd);
> > +			flush_tlb_pgtable(&init_mm, addr);
> > +			if (pmd_set_huge(pmd, phys_addr + addr, prot)) {
> > +				pmd_free_pte_page(&old_pmd);
> >   				continue;
> > +			} else
> > +				set_pmd(pmd, old_pmd);
> >   		}
> >   
>
> Can we have something like a pmd_can_set_huge() helper? Then we could
> avoid pointless modification and TLB invalidation work when
> pmd_set_huge() will fail.

Actually, pmd_set_huge() will never fail because, if
CONFIG_HAVE_ARCH_HUGE_VMAP is disabled, ioremap_pmd_enabled()
will fail and if enabled (i.e. ARM64 & x86), they don't fail
in their implementation. So, rather we can do the following.

-                       if (pmd_set_huge(pmd, phys_addr + addr, prot)) {
-                               pmd_free_pte_page(&old_pmd);
-                               continue;
-                       } else
-                               set_pmd(pmd, old_pmd);
+                       pmd_set_huge(pmd, phys_addr + addr, prot)
+                       pmd_free_pte_page(&old_pmd);
+                       continue;

> 	if (ioremap_pmd_enabled() &&
> 	    ((next - addr) == PMD_SIZE) &&
> 	    IS_ALIGNED(phys_addr + addr, PMD_SIZE) &&
> 	    pmd_can_set_huge(pmd, phys_addr + addr, prot)) {
> 	    	// clear entries, invalidate TLBs, and free tables
> 		...
> 		continue;
>
> 	}
>
> Thanks,
> MArk.
>
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Chintan
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