Hi Vincenzo, On Thu, Jan 23, 2020 at 10:48:07AM +0000, Vincenzo Frascino wrote: > Hi Boqun Feng, > > sorry for the late reply. > That's OK, thanks for your review ;-) > On 16/12/2019 00:19, Boqun Feng wrote: > > Hi, > > > > This is the RFC patchset for vDSO support in ARM64 Hyper-V guest. To > > test it, Michael's ARM64 support patchset: > > > > https://lore.kernel.org/linux-arm-kernel/1570129355-16005-1-git-send-email-mikelley@xxxxxxxxxxxxx/ > > > > is needed. > > > > Similar as x86, Hyper-V on ARM64 use a TSC page for guests to read > > the virtualized hardware timer, this TSC page is read-only for the > > guests, so could be used for vDSO data page. And the vDSO (userspace) > > code could use the same code for timer reading as kernel, since > > they read the same TSC page. > > > > I had a look to your patches and overall, I could not understand why we can't > use the arch_timer to do the same things you are doing with the one you > introduced in this series. What confuses me is that KVM works just fine with the > arch_timer which was designed with virtualization in mind. Why do we need > another one? Could you please explain? > Please note that the guest VM on Hyper-V for ARM64 doesn't use arch_timer as the clocksource. See: https://lore.kernel.org/linux-arm-kernel/1570129355-16005-7-git-send-email-mikelley@xxxxxxxxxxxxx/ , ACPI_SIG_GTDT is used for setting up Hyper-V synthetic clocksource and other initialization work. So just to be clear, your suggestion is 1) Hyper-V guest on ARM64 should use arch_timer as clocksource and vDSO will just work. or 2) Even though arch_timer is not used as the clocksource, we can still use it for vDSO. ? Regards, Boqun > > This patchset therefore extends ARM64's __vsdo_init() to allow multiple > > data pages and introduces the vclock_mode concept similar to x86 to > > allow different platforms (bare-metal, Hyper-V, etc.) to switch to > > different __arch_get_hw_counter() implementations. The rest of this > > patchset does the necessary setup for Hyper-V guests: mapping tsc page, > > enabling userspace to read cntvct, etc. to enable vDSO. > > > > This patchset consists of 6 patches: > > > > patch #1 allows hv_get_raw_timer() definition to be overridden for > > userspace and kernel to share the same hv_read_tsc_page() definition. > > > > patch #2 extends ARM64 to support multiple vDSO data pages. > > > > patch #3 introduces vclock_mode similiar to x86 to allow different > > __arch_get_hw_counter() implementations for different clocksources. > > > > patch #4 maps Hyper-V TSC page into vDSO data page. > > > > patch #5 allows userspace to read cntvct, so that userspace can > > efficiently read the clocksource. > > > > patch #6 enables the vDSO for ARM64 Hyper-V guest. > > > > The whole patchset is based on v5.5-rc1 plus Michael's ARM64 support > > patchset, and I've done a few tests with: > > > > https://github.com/nlynch-mentor/vdsotest > > > > Comments and suggestions are welcome! > > > > Regards, > > Boqun > > > > _______________________________________________ > > linux-arm-kernel mailing list > > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > > > > -- > Regards, > Vincenzo
