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Re: [PATCH 5/6] target/arm: Advertise FEAT_ETS for '-cpu max'


From: Richard Henderson
Subject: Re: [PATCH 5/6] target/arm: Advertise FEAT_ETS for '-cpu max'
Date: Fri, 19 Aug 2022 22:21:44 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0

On 8/19/22 04:00, Peter Maydell wrote:
The architectural feature FEAT_ETS (Enhanced Translation
Synchronization) is a set of tightened guarantees about memory
ordering involving translation table walks:

  * if memory access RW1 is ordered-before memory access RW2 then it
    is also ordered-before any translation table walk generated by RW2
    that generates a translation fault, address size fault or access
    fault

  * TLB maintenance on non-exec-permission translations is guaranteed
    complete after a DSB (ie it does not need the context
    synchronization event that you have to have if you don’t have
    FEAT_ETS)

For QEMU’s implementation we don’t reorder translation table walk
accesses, and we guarantee to finish the TLB maintenance as soon as
the TLB op is done (the tlb_flush functions will complete at the end
of the TLB, and TLB ops always end the TB because they’re sysreg

First TLB on this line should be TB.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~



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