linux-kernel - RE: [PATCH 7/7] arm64: Mark kernel page ranges contiguous

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Date:	Thu, 17 Sep 2015 10:33:39 -0700
From:	Jeremy Linton <Jeremy.Linton@....com>
To:	Steve Capper <steve.capper@...aro.org>
CC:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Steve Capper <Steve.Capper@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"dwoods@...hip.com" <dwoods@...hip.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Will Deacon <Will.Deacon@....com>,
	Shijie Huang <Shijie.Huang@....com>
Subject: RE: [PATCH 7/7] arm64: Mark kernel page ranges contiguous

|Hi Jeremy,
|One quick comment for now below.
|I ran into a problem testing this on my Seattle board, and needed the fix
|below.
<snip>
|> -       } while (pte++, addr += PAGE_SIZE, addr != end);
|> +               next = min(end, (addr + CONT_SIZE) & CONT_MASK);
|> +               if (((addr | next | phys) & CONT_RANGE_MASK) == 0) {
|> +                       /* a block of CONT_RANGE_SIZE PTEs */
|> +                       __populate_init_pte(pte, addr, next, phys,
|> +                                           prot | __pgprot(PTE_CONT));
|> +                       pte += CONT_RANGE;
|> +               } else {
|> +                       /*
|> +                        * If the range being split is already inside of a
|> +                        * contiguous range but this PTE isn't going to be
|> +                        * contiguous, then we want to unmark the adjacent
|> +                        * ranges, then update the portion of the range we
|> +                        * are interrested in.
|> +                        */
|> +                        clear_cont_pte_range(pte, addr);
|> +                        __populate_init_pte(pte, addr, next, phys, prot);
|> +                        pte += CONT_RANGE_OFFSET(next - addr);
|
|I think this should instead be:
|pte += (next - addr) >> PAGE_SHIFT;
|
|Without the above change, I get panics on boot with my Seattle board when
|efi_rtc is initialised.
|(I think the EFI runtime stuff exacerbates the non-contiguous code path
|hence I notice it on my system).

I think that implies you have linear mappings >= 2M that aren’t aligned. Ok, but that almost sounds like something we want to complain about if we detect it.






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