Re: [PATCH 1/2] arm64: Get existing page protections in split_pmd

[Laura Abbott]

On 11/05/2015 02:15 AM, Xishi Qiu wrote:
> On 2015/11/4 5:48, Laura Abbott wrote:
>
> > Rather than always putting the least restrictived permissions
> > (PAGE_KERNEL_EXEC) when spliting a pmd into pages, use
> > the existing permissions from the pmd for the page.
> >
> > Signed-off-by: Laura Abbott <labbott@xxxxxxxxxxxxxxxxx>
> > ---
> >   arch/arm64/mm/mmu.c | 9 ++++-----
> >   1 file changed, 4 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > index 9211b85..ff41efa 100644
> > --- a/arch/arm64/mm/mmu.c
> > +++ b/arch/arm64/mm/mmu.c
> > @@ -75,14 +75,13 @@ static void __init *early_alloc(unsigned long sz)
> >   static void split_pmd(pmd_t *pmd, pte_t *pte)
> >   {
> >   	unsigned long pfn = pmd_pfn(*pmd);
> > +	unsigned long addr = pfn << PAGE_SHIFT;
> > +	pgprot_t prot = __pgprot(pmd_val(*pmd) ^ addr) | PTE_TYPE_PAGE;
> > +
>
> Hi Laura,
>
> I'm not quite understand, I find split_pud() doesn't set the flag
> PMD_TYPE_TABLE. If we clear xx_TABLE_BIT, does that means the page
> is large page?

I'm assuming by large page you mean a block mapping. Yes, without
that entry the kernel treats this as a block mapping

> And what is the different from the flag xx_TYPE_SECT?

That would mark it this as a block mapping which is not what we want
here.

> Thanks,
> Xishi Qiu



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