Hi Marc, Jianyong,

On Tue, Mar 30, 2021 at 4:56 PM Marc Zyngier [off-list ref] wrote:

From: Jianyong Wu <redacted>

Currently, there is no mechanism to keep time sync between guest and host
in arm/arm64 virtualization environment. Time in guest will drift compared
with host after boot up as they may both use third party time sources
to correct their time respectively. The time deviation will be in order
of milliseconds. But in some scenarios,like in cloud environment, we ask
for higher time precision.

kvm ptp clock, which chooses the host clock source as a reference
clock to sync time between guest and host, has been adopted by x86
which takes the time sync order from milliseconds to nanoseconds.

This patch enables kvm ptp clock for arm/arm64 and improves clock sync precision
significantly.

Why does this not depend on KVM_GUEST on ARM?
I.e. shouldn't the dependency be:

    KVM_GUEST && (X86 || (HAVE_ARM_SMCCC_DISCOVERY && ARM_ARCH_TIMER))

?

        default y
        help
          This driver adds support for using kvm infrastructure as a PTP

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds