Re: [Qemu-devel] Tracing guest virtual addresses

[Peter Maydell <peter.maydell@linaro.org>]

On 26 June 2017 at 13:04, Lluís Vilanova <vilanova@ac.upc.edu> wrote:
> Peter Maydell writes:
>
>> On 26 June 2017 at 10:26, Lluís Vilanova <vilanova@ac.upc.edu> wrote:
>>> There's two places where memory access tracing is triggered:
>>>
>>> * tcg_gen_qemu_ld/st_...
>>> * ld/st templates (both softmmu and user)
>>>
>>> AFAIK, helpers use the ld/st templates to access guest memory.
>
>> Mostly, but there are one or two special cases, for instance
>> the ARM HELPER(dc_zva) in target/arm/helper.c, which has a
>> fastpath that uses tlb_vaddr_to_host to look up the host memory
>> address and then memset to do the clear-to-zeroes operation.
>
> Should that be replaced with a cpu_memset or similar?

Possibly -- PPC and S390 also have a fast-memset like this
(and S390 also has a fast-memmove). However I would be wary
of there being architecture-specific corner cases (eg
needing to get the right vaddr for a fault if the accesses
fault).

thanks
-- PMM