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Re: [Qemu-devel] [PATCH v2 for-2.11 0/2] Fix TCG atomic writes to nondir

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH v2 for-2.11 0/2] Fix TCG atomic writes to nondirty pages
Date: Mon, 20 Nov 2017 21:54:37 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0

On 20/11/2017 19:08, Peter Maydell wrote:
> To do a write to memory that is marked as notdirty, we need
> to invalidate any TBs we have cached for that memory, and
> update the cpu physical memory dirty flags for VGA and migration.
> The slowpath code in notdirty_mem_write() does all this correctly,
> but the new atomic handling code in atomic_mmu_lookup() doesn't
> do anything at all, it just clears the dirty bit in the TLB.
> The effect of this bug is that if the first write to a notdirty
> page for which we have cached TBs is by a guest atomic access,
> we fail to invalidate the TBs and subsequently will execute
> incorrect code. This can be seen by trying to run 'javac' on AArch64.
> The first patch here refactors notdirty_mem_write() to pull out
> the "correctly handle dirty bit updates" parts of the code into
> two new functions memory_notdirty_write_prepare() and
> memory_notdirty_write_complete(). The second patch then uses
> those functions to fix the atomic helpers.

Reviewed-by: Paolo Bonzini <address@hidden>



> Changes v1->v2:
>  * add the 'bool active;' flag to NotDirtyInfo in patch 1
>  * change the comment on NotDirtyInfo in patch 1 to document
>    the active flag (and to fix incorrect references to function
>    names that I forgot to update when I decided on the names for
>    the prepare/complete functions)
>  * in patch 2, don't call prepare unless the TLB was notdirty
>  * in patch 2, use the active flag to track whether we need to
>    call complete or not
> thanks
> -- PMM
> Peter Maydell (2):
>   exec.c: Factor out before/after actions for notdirty memory writes
>   accel/tcg: Handle atomic accesses to notdirty memory correctly
>  accel/tcg/atomic_template.h    | 12 ++++++++
>  include/exec/memory-internal.h | 62 ++++++++++++++++++++++++++++++++++++++++
>  accel/tcg/cputlb.c             | 38 +++++++++++++++---------
>  accel/tcg/user-exec.c          |  1 +
>  exec.c                         | 65 
> ++++++++++++++++++++++++++++--------------
>  5 files changed, 144 insertions(+), 34 deletions(-)

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