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Re: [Qemu-devel] [PATCH v7 17/27] cputlb: atomically update tlb fields u

From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH v7 17/27] cputlb: atomically update tlb fields used by tlb_reset_dirty
Date: Mon, 23 Jan 2017 11:17:27 -0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0

On 01/19/2017 09:04 AM, Alex Bennée wrote:
> The main use case for tlb_reset_dirty is to set the TLB_NOTDIRTY flags
> in TLB entries to force the slow-path on writes. This is used to mark
> page ranges containing code which has been translated so it can be
> invalidated if written to. To do this safely we need to ensure the TLB
> entries in question for all vCPUs are updated before we attempt to run
> the code otherwise a race could be introduced.
> To achieve this we atomically set the flag in tlb_reset_dirty_range and
> take care when setting it when the TLB entry is filled.
> On 32 bit systems attempting to emulate 64 bit guests we don't even
> bother as we might not have the atomic primitives available. MTTCG is
> disabled in this case and can't be forced on. The copy_tlb_helper
> function helps keep the atomic semantics in one place to avoid
> confusion.
> The dirty helper function is made static as it isn't used outside of
> cputlb.
> Signed-off-by: Alex Bennée <address@hidden>

Reviewed-by: Richard Henderson <address@hidden>


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