From: Julien Grall <julien.grall@arm.com>
To: Shanker Donthineni <shankerd@codeaurora.org>,
Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
xen-devel@lists.xensource.com
Cc: Vikram Sethi <vikrams@codeaurora.org>,
Philip Elcan <pelcan@codeaurora.org>,
Ian Campbell <ian.campbell@citrix.com>,
Jan Beulich <jbeulich@suse.com>
Subject: Re: [PATCH] xen: arm: zero EL2 pagetable pages before use
Date: Mon, 14 Mar 2016 07:37:08 +0000 [thread overview]
Message-ID: <56E66A24.3090104@arm.com> (raw)
In-Reply-To: <1457647206-9436-1-git-send-email-shankerd@codeaurora.org>
Hi Shanker,
On 11/03/2016 05:00, Shanker Donthineni wrote:
> From: Vikram Sethi <vikrams@codeaurora.org>
>
> arch/arm/mm.c has 2 uses of alloc_boot_pages which are used for
> pagetables, but the allocated pages are not zeroed. This can cause
> crashes on CPUs with aggressive prefetching when they find 'valid'
> entries in the page tables but which are really uninitialized.
> Memset the allocated pages before use.
I first thought the problem was related to break-before-make mandate by
the ARM architecture (see D4-1732 in ARM DDI 0487A.i) when the page
tables are modified in a certain way, but neither the frame table noor
the xen heap are used before the TLBs are nuked.
I would like to see more details in the commit message about the crash
and why (based on the spec) clearing the page is the right solution.
Note that I think clearing the page is good to avoid polluting the TLBs
with bogus entries and get better crash log.
> Change-Id: I517ca45ca240766dfbf1d6884c044c377babab7d
What this line for?
> Signed-off-by: Vikram Sethi <vikrams@codeaurora.org>
> Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
> ---
> xen/arch/arm/mm.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index 81f9e2e..215ec93 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -730,6 +730,7 @@ void __init setup_xenheap_mappings(unsigned long base_mfn,
> else
> {
> unsigned long first_mfn = alloc_boot_pages(1, 1);
> + memset(mfn_to_virt(first_mfn), 0, PAGE_SIZE);
You can move "first = mfn_to_virt(first_mfn)" earlier and re-use first here.
> pte = mfn_to_xen_entry(first_mfn, WRITEALLOC);
> pte.pt.table = 1;
> write_pte(p, pte);
> @@ -771,6 +772,7 @@ void __init setup_frametable_mappings(paddr_t ps, paddr_t pe)
> nr_second = frametable_size >> SECOND_SHIFT;
> second_base = alloc_boot_pages(nr_second, 1);
> second = mfn_to_virt(second_base);
> + memset(second, 0, nr_second * PAGE_SIZE);
> for ( i = 0; i < nr_second; i++ )
> {
> pte = mfn_to_xen_entry(second_base + i, WRITEALLOC);
>
Regards,
--
Julien Grall
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prev parent reply other threads:[~2016-03-14 7:37 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-10 22:00 [PATCH] xen: arm: zero EL2 pagetable pages before use Shanker Donthineni
2016-03-11 11:29 ` Jan Beulich
2016-03-11 12:56 ` Andrew Cooper
2016-03-11 13:13 ` Jan Beulich
2016-03-11 13:24 ` Andrew Cooper
2016-03-12 16:03 ` Julien Grall
2016-03-14 17:18 ` Shanker Donthineni
2016-03-15 17:37 ` Julien Grall
2016-03-12 14:32 ` Julien Grall
2016-03-14 7:37 ` Julien Grall [this message]
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