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Re: [Qemu-devel] [PATCH] translate-all: fix locking of TBs whose two pag

From: Max Filippov
Subject: Re: [Qemu-devel] [PATCH] translate-all: fix locking of TBs whose two pages share the same physical page
Date: Mon, 25 Jun 2018 09:46:53 -0700

On Mon, Jun 25, 2018 at 9:31 AM, Emilio G. Cota <address@hidden> wrote:
> Commit 0b5c91f ("translate-all: use per-page locking in !user-mode",
> 2018-06-15) introduced per-page locking. It assumed that the physical
> pages corresponding to a TB (at most two pages) are always distinct,
> which is wrong. For instance, an xtensa test provided by Max Filippov
> is broken by the commit, since the test maps two virtual pages
> to the same physical page:
>         virt1: 7fff, virt2: 8000
>         phys1 6000fff, phys2 6000000
> Fix it by removing the assumption from page_lock_pair.
> If the two physical page addresses are equal, we only lock
> the PageDesc once. Note that the two callers of page_lock_pair,
> namely page_unlock_tb and tb_link_page, are also updated so that
> we do not try to unlock the same PageDesc twice.
> Fixes: 0b5c91f74f3c83a36f37740969df8c775c997e69
> Reported-by: Max Filippov <address@hidden>
> Signed-off-by: Emilio G. Cota <address@hidden>
> ---
>  accel/tcg/translate-all.c | 32 +++++++++++++++++++++++++-------
>  1 file changed, 25 insertions(+), 7 deletions(-)

Tested-by: Max Filippov <address@hidden>
Thank you!

-- Max

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