kernel/arch/powerpc/include/asm/kvm_host.h, branch linux-4.3.y

powerpc: Revert "Use the POWER8 Micro Partition Prefetch Engine in KVM HV on POWER8"

2015-10-21T09:50:30Z

This reverts commit 9678cdaae939 ("Use the POWER8 Micro Partition Prefetch Engine in KVM HV on POWER8") because the original commit had multiple, partly self-cancelling bugs, that could cause occasional memory corruption. In fact the logmpp instruction was incorrectly using register r0 as the source of the buffer address and operation code, and depending on what was in r0, it would either do nothing or corrupt the 64k page pointed to by r0. The logmpp instruction encoding and the operation code definitions could be corrected, but then there is the problem that there is no clearly defined way to know when the hardware has finished writing to the buffer. The original commit attempted to work around this by aborting the write-out before starting the prefetch, but this is ineffective in the case where the virtual core is now executing on a different physical core from the one where the write-out was initiated. These problems plus advice from the hardware designers not to use the function (since the measured performance improvement from using the feature was actually mostly negative), mean that reverting the code is the best option. Fixes: 9678cdaae939 ("Use the POWER8 Micro Partition Prefetch Engine in KVM HV on POWER8") Signed-off-by: Paul Mackerras Signed-off-by: Michael Ellerman

KVM: disable halt_poll_ns as default for s390x

2015-09-25T08:31:30Z

We observed some performance degradation on s390x with dynamic halt polling. Until we can provide a proper fix, let's enable halt_poll_ns as default only for supported architectures. Architectures are now free to set their own halt_poll_ns default value. Signed-off-by: David Hildenbrand Signed-off-by: Paolo Bonzini

KVM: add halt_attempted_poll to VCPU stats

2015-09-16T10:17:00Z

This new statistic can help diagnosing VCPUs that, for any reason, trigger bad behavior of halt_poll_ns autotuning. For example, say halt_poll_ns = 480000, and wakeups are spaced exactly like 479us, 481us, 479us, 481us. Then KVM always fails polling and wastes 10+20+40+80+160+320+480 = 1110 microseconds out of every 479+481+479+481+479+481+479 = 3359 microseconds. The VCPU then is consuming about 30% more CPU than it would use without polling. This would show as an abnormally high number of attempted polling compared to the successful polls. Acked-by: Christian Borntraeger Signed-off-by: Paolo Bonzini

KVM: PPC: Book3S: Fix size of the PSPB register

2015-09-03T06:09:09Z

The size of the Problem State Priority Boost Register is only 32 bits, but the kvm_vcpu_arch->pspb variable is declared as "ulong", ie. 64-bit. However, the assembler code accesses this variable with 32-bit accesses, and the KVM_REG_PPC_PSPB macro is defined with SIZE_U32, too, so that the current code is broken on big endian hosts: kvmppc_get_one_reg_hv() will only return zero for this register since it is using the wrong half of the pspb variable. Let's fix this problem by adjusting the size of the pspb field in the kvm_vcpu_arch structure. Signed-off-by: Thomas Huth Signed-off-by: Paul Mackerras

KVM: PPC: Book3S HV: Fix bug in dirty page tracking

2015-08-22T09:16:18Z

This fixes a bug in the tracking of pages that get modified by the guest. If the guest creates a large-page HPTE, writes to memory somewhere within the large page, and then removes the HPTE, we only record the modified state for the first normal page within the large page, when in fact the guest might have modified some other normal page within the large page. To fix this we use some unused bits in the rmap entry to record the order (log base 2) of the size of the page that was modified, when removing an HPTE. Then in kvm_test_clear_dirty_npages() we use that order to return the correct number of modified pages. The same thing could in principle happen when removing a HPTE at the host's request, i.e. when paging out a page, except that we never page out large pages, and the guest can only create large-page HPTEs if the guest RAM is backed by large pages. However, we also fix this case for the sake of future-proofing. The reference bit is also subject to the same loss of information. We don't make the same fix here for the reference bit because there isn't an interface for userspace to find out which pages the guest has referenced, whereas there is one for userspace to find out which pages the guest has modified. Because of this loss of information, the kvm_age_hva_hv() and kvm_test_age_hva_hv() functions might incorrectly say that a page has not been referenced when it has, but that doesn't matter greatly because we never page or swap out large pages. Signed-off-by: Paul Mackerras Signed-off-by: Alexander Graf

KVM: PPC: Book3S HV: Implement dynamic micro-threading on POWER8

2015-08-22T09:16:17Z

This builds on the ability to run more than one vcore on a physical core by using the micro-threading (split-core) modes of the POWER8 chip. Previously, only vcores from the same VM could be run together, and (on POWER8) only if they had just one thread per core. With the ability to split the core on guest entry and unsplit it on guest exit, we can run up to 8 vcpu threads from up to 4 different VMs, and we can run multiple vcores with 2 or 4 vcpus per vcore. Dynamic micro-threading is only available if the static configuration of the cores is whole-core mode (unsplit), and only on POWER8. To manage this, we introduce a new kvm_split_mode struct which is shared across all of the subcores in the core, with a pointer in the paca on each thread. In addition we extend the core_info struct to have information on each subcore. When deciding whether to add a vcore to the set already on the core, we now have two possibilities: (a) piggyback the vcore onto an existing subcore, or (b) start a new subcore. Currently, when any vcpu needs to exit the guest and switch to host virtual mode, we interrupt all the threads in all subcores and switch the core back to whole-core mode. It may be possible in future to allow some of the subcores to keep executing in the guest while subcore 0 switches to the host, but that is not implemented in this patch. This adds a module parameter called dynamic_mt_modes which controls which micro-threading (split-core) modes the code will consider, as a bitmap. In other words, if it is 0, no micro-threading mode is considered; if it is 2, only 2-way micro-threading is considered; if it is 4, only 4-way, and if it is 6, both 2-way and 4-way micro-threading mode will be considered. The default is 6. With this, we now have secondary threads which are the primary thread for their subcore and therefore need to do the MMU switch. These threads will need to be started even if they have no vcpu to run, so we use the vcore pointer in the PACA rather than the vcpu pointer to trigger them. It is now possible for thread 0 to find that an exit has been requested before it gets to switch the subcore state to the guest. In that case we haven't added the guest's timebase offset to the timebase, so we need to be careful not to subtract the offset in the guest exit path. In fact we just skip the whole path that switches back to host context, since we haven't switched to the guest context. Signed-off-by: Paul Mackerras Signed-off-by: Alexander Graf

KVM: PPC: Book3S HV: Make use of unused threads when running guests

2015-08-22T09:16:17Z

When running a virtual core of a guest that is configured with fewer threads per core than the physical cores have, the extra physical threads are currently unused. This makes it possible to use them to run one or more other virtual cores from the same guest when certain conditions are met. This applies on POWER7, and on POWER8 to guests with one thread per virtual core. (It doesn't apply to POWER8 guests with multiple threads per vcore because they require a 1-1 virtual to physical thread mapping in order to be able to use msgsndp and the TIR.) The idea is that we maintain a list of preempted vcores for each physical cpu (i.e. each core, since the host runs single-threaded). Then, when a vcore is about to run, it checks to see if there are any vcores on the list for its physical cpu that could be piggybacked onto this vcore's execution. If so, those additional vcores are put into state VCORE_PIGGYBACK and their runnable VCPU threads are started as well as the original vcore, which is called the master vcore. After the vcores have exited the guest, the extra ones are put back onto the preempted list if any of their VCPUs are still runnable and not idle. This means that vcpu->arch.ptid is no longer necessarily the same as the physical thread that the vcpu runs on. In order to make it easier for code that wants to send an IPI to know which CPU to target, we now store that in a new field in struct vcpu_arch, called thread_cpu. Reviewed-by: David Gibson Tested-by: Laurent Vivier Signed-off-by: Paul Mackerras Signed-off-by: Alexander Graf

KVM: add memslots argument to kvm_arch_memslots_updated

2015-05-26T10:40:17Z

Prepare for the case of multiple address spaces. Reviewed-by: Radim Krcmar Signed-off-by: Paolo Bonzini

Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm

2015-04-26T20:06:22Z

Pull second batch of KVM changes from Paolo Bonzini: "This mostly includes the PPC changes for 4.1, which this time cover Book3S HV only (debugging aids, minor performance improvements and some cleanups). But there are also bug fixes and small cleanups for ARM, x86 and s390. The task_migration_notifier revert and real fix is still pending review, but I'll send it as soon as possible after -rc1" * tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (29 commits) KVM: arm/arm64: check IRQ number on userland injection KVM: arm: irqfd: fix value returned by kvm_irq_map_gsi KVM: VMX: Preserve host CR4.MCE value while in guest mode. KVM: PPC: Book3S HV: Use msgsnd for signalling threads on POWER8 KVM: PPC: Book3S HV: Translate kvmhv_commence_exit to C KVM: PPC: Book3S HV: Streamline guest entry and exit KVM: PPC: Book3S HV: Use bitmap of active threads rather than count KVM: PPC: Book3S HV: Use decrementer to wake napping threads KVM: PPC: Book3S HV: Don't wake thread with no vcpu on guest IPI KVM: PPC: Book3S HV: Get rid of vcore nap_count and n_woken KVM: PPC: Book3S HV: Move vcore preemption point up into kvmppc_run_vcpu KVM: PPC: Book3S HV: Minor cleanups KVM: PPC: Book3S HV: Simplify handling of VCPUs that need a VPA update KVM: PPC: Book3S HV: Accumulate timing information for real-mode code KVM: PPC: Book3S HV: Create debugfs file for each guest's HPT KVM: PPC: Book3S HV: Add ICP real mode counters KVM: PPC: Book3S HV: Move virtual mode ICP functions to real-mode KVM: PPC: Book3S HV: Convert ICS mutex lock to spin lock KVM: PPC: Book3S HV: Add guest->host real mode completion counters KVM: PPC: Book3S HV: Add helpers for lock/unlock hpte ...

KVM: PPC: Book3S HV: Use bitmap of active threads rather than count

2015-04-21T13:21:33Z

Currently, the entry_exit_count field in the kvmppc_vcore struct contains two 8-bit counts, one of the threads that have started entering the guest, and one of the threads that have started exiting the guest. This changes it to an entry_exit_map field which contains two bitmaps of 8 bits each. The advantage of doing this is that it gives us a bitmap of which threads need to be signalled when exiting the guest. That means that we no longer need to use the trick of setting the HDEC to 0 to pull the other threads out of the guest, which led in some cases to a spurious HDEC interrupt on the next guest entry. Signed-off-by: Paul Mackerras Signed-off-by: Alexander Graf