On Fri, Feb 3, 2017 at 2:14 PM, Jintack Lim <jintack@xxxxxxxxxxxxxxx> wrote: > On Fri, Feb 3, 2017 at 7:33 AM, Christoffer Dall <cdall@xxxxxxxxxx> wrote: >> On Thu, Feb 02, 2017 at 09:51:13AM -0500, Jintack Lim wrote: >>> On Thu, Feb 2, 2017 at 7:31 AM, Christoffer Dall <cdall@xxxxxxxxxx> wrote: >>> > Hi Jintack, >>> > >>> > On Wed, Feb 01, 2017 at 12:43:00PM -0500, Jintack Lim wrote: >>> >> The ARM architecture defines the EL1 physical timer and the virtual timer, >>> >> and it is reasonable for an OS to expect to be able to access both. >>> >> However, the current KVM implementation does not provide the EL1 physical >>> >> timer to VMs but terminates VMs on access to the timer. >>> >> >>> >> This patch series enables VMs to use the EL1 physical timer through >>> >> trap-and-emulate. The KVM host emulates each EL1 physical timer register >>> >> access and sets up the background timer accordingly. When the background >>> >> timer expires, the KVM host injects EL1 physical timer interrupts to the >>> >> VM. Alternatively, it's also possible to allow VMs to access the EL1 >>> >> physical timer without trapping. However, this requires somehow using the >>> >> EL2 physical timer for the Linux host while running the VM instead of the >>> >> EL1 physical timer. Right now I just implemented trap-and-emulate because >>> >> this was straightforward to do, and I leave it to future work to determine >>> >> if transferring the EL1 physical timer state to the EL2 timer provides any >>> >> performance benefit. >>> >> >>> >> This feature will be useful for any OS that wishes to access the EL1 >>> >> physical timer. Nested virtualization is one of those use cases. A nested >>> >> hypervisor running inside a VM would think it has full access to the >>> >> hardware and naturally tries to use the EL1 physical timer as Linux would >>> >> do. Other nested hypervisors may try to use the EL2 physical timer as Xen >>> >> would do, but supporting the EL2 physical timer to the VM is out of scope >>> >> of this patch series. This patch series will make it easy to add the EL2 >>> >> timer support in the future, though. >>> >> >>> >> Note that Linux VMs booting in EL1 will be unaffected by this patch series >>> >> and will continue to use only the virtual timer and this patch series will >>> >> therefore not introduce any performance degredation as a result of >>> >> trap-and-emulate. >>> >> >>> >> v2 => v3: >>> >> - Rebase on kvmarm/queue >>> >> - Take kvm->lock to synchronize cntvoff across all vtimers >>> >> - Remove unnecessary function parameters >>> >> - Add comments >>> > >>> > I just gave v3 a test run on my TC2 (32-bit platform) and my guest >>> > quickly locks up trying to run cyclictest or when booting the machine it >>> > stalls with RCU timeouts. >>> >>> Ok. It's my fault not to specify that the emulated physical timer is >>> supported/tested on arm64. >>> On 32-bit platform, it is supposed to show the same behavior as >>> before, but I haven't tested. >>> Were you using the physical timer or the virtual timer for the guest? >>> >>> > >>> > Could you have a look? >>> >>> Sure, I'll have a look. I don't have access to my Cubietruck today, >>> but I can work on that tomorrow. >>> >> >> Don't bother, I've figured this out for you. > > Thanks a lot. > >> >> You need the following fixup to your patch: > > Ok. I'll post v4 soon. > You've already do "acked-by" for this commit. Do I need to change it > to "signed-off-by"? > I guess so, technically. I don't care deeply though. -Christoffer
