linux-kernel - Re: [4/4] MIPS: Sync icache & dcache in set_pte

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Date:	Wed, 2 Mar 2016 19:03:35 -0800
From:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
To:	Paul Burton <paul.burton@...tec.com>, <linux-mips@...ux-mips.org>
CC:	Lars Persson <lars.persson@...s.com>,
	"stable # v4 . 1+" <stable@...r.kernel.org>,
	"Steven J. Hill" <Steven.Hill@...tec.com>,
	"David Daney" <david.daney@...ium.com>,
	Huacai Chen <chenhc@...ote.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	<linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jerome Marchand <jmarchan@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [4/4] MIPS: Sync icache & dcache in set_pte_at

Paul Burton wrote:

> It is, however, used in such a way by others & seems to me like the only
> correct way to implement the lazy cache flushing. The alternative would
> be to adjust all generic code to ensure flush_icache_page gets called
> before set_pte_at

... which is an exact case right now. Both calls of flush_icache_page() are:

1) do_swap_page()

         flush_icache_page(vma, page);
         if (pte_swp_soft_dirty(orig_pte))
                 pte = pte_mksoft_dirty(pte);
         set_pte_at(mm, address, page_table, pte);
...

2) do_set_pte()

         flush_icache_page(vma, page);
         entry = mk_pte(page, vma->vm_page_prot);
         if (write)
                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
         if (anon) {
                 inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
                 page_add_new_anon_rmap(page, vma, address);
         } else {
                 inc_mm_counter_fast(vma->vm_mm, MM_FILEPAGES);
                 page_add_file_rmap(page);
         }
         set_pte_at(vma->vm_mm, address, pte, entry);

         /* no need to invalidate: a not-present page won't be cached */
         update_mmu_cache(vma, address, pte);
....

You should only be sure that flush_icache_page() completes a lazy 
D-cache flush.

- Leonid.