Re: [Xen-devel] [PATCH 11/11] xen/mmu: Release just the MFN list, not MFN list and part of pagetables.

From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>
Subject: Re: [Xen-devel] [PATCH 11/11] xen/mmu: Release just the MFN list, not MFN list and part of pagetables.
Date: Tue, 21 Aug 2012 15:18:26 +0100	[thread overview]
Message-ID: <alpine.DEB.2.02.1208211514130.15568@kaball.uk.xensource.com> (raw)
In-Reply-To: <1345133009-21941-12-git-send-email-konrad.wilk@oracle.com>

On Thu, 16 Aug 2012, Konrad Rzeszutek Wilk wrote:
> We call memblock_reserve for [start of mfn list] -> [PMD aligned end
> of mfn list] instead of <start of mfn list> -> <page aligned end of mfn list].
> 
> This has the disastrous effect that if at bootup the end of mfn_list is
> not PMD aligned we end up returning to memblock parts of the region
> past the mfn_list array. And those parts are the PTE tables with
> the disastrous effect of seeing this at bootup:

This patch looks wrong to me.

Aren't you changing the way mfn_list is reserved using memblock in patch
#3? Moreover it really seems to me that you are PAGE_ALIGN'ing size
rather than PMD_ALIGN'ing it there.

> Write protecting the kernel read-only data: 10240k
> Freeing unused kernel memory: 1860k freed
> Freeing unused kernel memory: 200k freed
> (XEN) mm.c:2429:d0 Bad type (saw 1400000000000002 != exp 7000000000000000) for mfn 116a80 (pfn 14e26)
> ...
> (XEN) mm.c:908:d0 Error getting mfn 116a83 (pfn 14e2a) from L1 entry 8000000116a83067 for l1e_owner=0, pg_owner=0
> (XEN) mm.c:908:d0 Error getting mfn 4040 (pfn 5555555555555555) from L1 entry 0000000004040601 for l1e_owner=0, pg_owner=0
> .. and so on.
>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> ---
>  arch/x86/xen/mmu.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index 5a880b8..6019c22 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -1227,7 +1227,6 @@ static void __init xen_pagetable_setup_done(pgd_t *base)
>  			/* We should be in __ka space. */
>  			BUG_ON(xen_start_info->mfn_list < __START_KERNEL_map);
>  			addr = xen_start_info->mfn_list;
> -			size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
>  			/* We roundup to the PMD, which means that if anybody at this stage is
>  			 * using the __ka address of xen_start_info or xen_start_info->shared_info
>  			 * they are in going to crash. Fortunatly we have already revectored
> @@ -1235,6 +1234,7 @@ static void __init xen_pagetable_setup_done(pgd_t *base)
>  			size = roundup(size, PMD_SIZE);
>  			xen_cleanhighmap(addr, addr + size);
>  
> +			size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
>  			memblock_free(__pa(xen_start_info->mfn_list), size);
>  			/* And revector! Bye bye old array */
>  			xen_start_info->mfn_list = new_mfn_list;
> -- 
> 1.7.7.6
> 
> 
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