Hi Geert,

On 2021-05-11 10:07, Geert Uytterhoeven wrote:

Hi Marc, Jianyong,

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

quoted

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.

quoted

--- a/drivers/ptp/Kconfig
+++ b/drivers/ptp/Kconfig

@@ -108,7 +108,7 @@ config PTP_1588_CLOCK_PCH
 config PTP_1588_CLOCK_KVM
        tristate "KVM virtual PTP clock"
        depends on PTP_1588_CLOCK
-       depends on KVM_GUEST && X86
+       depends on (KVM_GUEST && X86) || (HAVE_ARM_SMCCC_DISCOVERY && 

ARM_ARCH_TIMER)

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))

?

arm/arm64 do not select KVM_GUEST. Any kernel can be used for a guest,
and KVM/arm64 doesn't know about this configuration symbol.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

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