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

[Richard Henderson]

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>


r~