Hi Ard,
On 2020.02.25 22:27, Ard Biesheuvel wrote:
On Tue, 25 Feb 2020 at 19:31, Ard Biesheuvel <ard.biesheu...@linaro.org> wrote:
On Tue, 25 Feb 2020 at 19:28, Ard Biesheuvel <ard.biesheu...@linaro.org> wrote:
Cache maintenance operations by set/way are only intended to be used
in the context of on/offlining a core, while it has been taken out of
the coherency domain. Any use intended to ensure that the contents of
the cache have made it to main memory is unreliable, since cacheline
migration and non-architected system caches may cause these contents
to linger elsewhere, without being visible in main memory once the
MMU and caches are disabled.
In KVM on Linux, there are horrid hacks in place to ensure that such
set/way operations are trapped, and replaced with a single by-VA
clean/invalidate of the entire guest VA space once the MMU state
changes, which can be costly, and is unnecessary if we manage the
caches a bit more carefully, and perform maintenance by virtual
address only.
So let's get rid of the call to ArmInvalidateDataCache () in the
PrePeiCore startup code, and instead, invalidate the UEFI memory
region by virtual address, which is the only memory region we will
be touching with the caches and MMU both disabled and enabled.
(This will lead to data corruption if data written with the MMU off
is shadowed by clean, stale cachelines that stick around when the
MMU is enabled again.)
Signed-off-by: Ard Biesheuvel <ard.biesheu...@linaro.org>
---
Forgot to add a note that this is the *PrePi* version, not the
PrePeiCore one that I sent before.
@Pete: this might affect RPi3 and RPi4, and I am currently not able to
test it. If it's not too much trouble, I'd appreciate a Tested-by. If
not, I'll test it myself, but it may take me a while to get around to
it.
Actually, I decided to dedicate some of my evening to have a go at this myself.
This patch works for me on RPi4, as well as the BCM GENET with the
latest changes, and the version of the driver that turned up in
net-next today
I am getting around 100 - 150 Mbit/s - is that what I should expect?
Not sure what device you're running your system from, because I'm easily
reaching 700 Mbit/s when running a large Samba copy from a USB 3.0
drive, which I hope should work well enough as a stress test.
Tested both for read and write, with and without the patch (but only on
Pi 4). No noticeable reduction in speed as far as I can tell.
With this:
Tested-By: Pete Batard <p...@akeo.ie>
Regards,
/Pete
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