On 06/02/2017 02:11 AM, Marc Zyngier wrote:
On 01/06/17 22:00, David Daney wrote:
On 06/01/2017 03:20 AM, Marc Zyngier wrote:
Some systems have less than perfect GICv3 implementations, leading to
all kind of ugly issues (guest hanging, host dying). In order to allow
some level of diagnostic, and in some cases implement workarounds,
this series enables the trapping of both Group-0, Group-1 and Common
sysregs. Mediating the access at EL2 allows some form of sanity
checking that the HW is sometimes sorely lacking.
Instead of fully emulating a GICv3 CPU interface, we still use the
existing HW (list registers, AP registers, VMCR...), which allows the
code to be independent from the rest of the KVM code, and to cope with
partial trapping.
Of course, trapping has a cost, which is why this must be either
enabled on the command line, or selected by another cpu capability
(see Cavium erratum 30115). A quick test on an A57-based platform
shows a 25% hit when repeatedly banging on the trapped registers,
while normal workloads do not seem to suffer noticeably from such
trapping (hackbench variance is in the usual noise, despite being very
IPI happy).
This has been tested on a dual socket Thundex-X and a Freescale LS-2085a.
I've taken the liberty to rebase David Daney's initial Cavium erratum
30115 workaround on top of this series, and included it here as a
typical use case.
I pulled this from:
https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=kvm-arm64/gicv3-cpuif-mediated-access
this morning at commit 58c1763c5aa6223ab3d04e0c183a31eb0aef832e
Entire series tested by and
Acked-by: David Daney <david.daney@xxxxxxxxxx>
Thanks David. May I ask what particular system this was tested on (just
so that I have a additional reference point)?
Sure, Unfortunatly I think it doesn't really increase your testing coverage.
I tested on a 2-node NUMA Cavium cn8890 (ThunderX). This chassis is
known as CRB-2S. Running Ubuntu 16.04.2 userspace.
First I verified that a kernel built from clean v4.12-rc3 would fail
with symptoms of no interrupts being processed while running a heavy KVM
start/stop workload. It does, we get a failure in under 5 minutes.
Then I applied your 25 patch set, and retested. With the patch set
applied, no failures were observed after more than 4 hours.
Cheers,
M.
