This is a note to let you know that I've just added the patch titled KVM: PPC: Tick accounting should defer vtime accounting 'til after IRQ handling to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-ppc-tick-accounting-should-defer-vtime-accountin.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 3aeed0c876227b61e7852f8a6345234a77261be9 Author: Laurent Vivier <lvivier@xxxxxxxxxx> Date: Thu Oct 28 00:21:50 2021 +1000 KVM: PPC: Tick accounting should defer vtime accounting 'til after IRQ handling [ Upstream commit 235cee162459d96153d63651ce7ff51752528c96 ] Commit 112665286d08 ("KVM: PPC: Book3S HV: Context tracking exit guest context before enabling irqs") moved guest_exit() into the interrupt protected area to avoid wrong context warning (or worse). The problem is that tick-based time accounting has not yet been updated at this point (because it depends on the timer interrupt firing), so the guest time gets incorrectly accounted to system time. To fix the problem, follow the x86 fix in commit 160457140187 ("Defer vtime accounting 'til after IRQ handling"), and allow host IRQs to run before accounting the guest exit time. In the case vtime accounting is enabled, this is not required because TB is used directly for accounting. Before this patch, with CONFIG_TICK_CPU_ACCOUNTING=y in the host and a guest running a kernel compile, the 'guest' fields of /proc/stat are stuck at zero. With the patch they can be observed increasing roughly as expected. Fixes: e233d54d4d97 ("KVM: booke: use __kvm_guest_exit") Fixes: 112665286d08 ("KVM: PPC: Book3S HV: Context tracking exit guest context before enabling irqs") Cc: stable@xxxxxxxxxxxxxxx # 5.12+ Signed-off-by: Laurent Vivier <lvivier@xxxxxxxxxx> [np: only required for tick accounting, add Book3E fix, tweak changelog] Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx> Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20211027142150.3711582-1-npiggin@xxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index d6c4e27f7ed9..1d2593238995 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -3399,7 +3399,20 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc) kvmppc_set_host_core(pcpu); - guest_exit_irqoff(); + context_tracking_guest_exit(); + if (!vtime_accounting_enabled_this_cpu()) { + local_irq_enable(); + /* + * Service IRQs here before vtime_account_guest_exit() so any + * ticks that occurred while running the guest are accounted to + * the guest. If vtime accounting is enabled, accounting uses + * TB rather than ticks, so it can be done without enabling + * interrupts here, which has the problem that it accounts + * interrupt processing overhead to the host. + */ + local_irq_disable(); + } + vtime_account_guest_exit(); local_irq_enable(); @@ -4236,7 +4249,20 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit, kvmppc_set_host_core(pcpu); - guest_exit_irqoff(); + context_tracking_guest_exit(); + if (!vtime_accounting_enabled_this_cpu()) { + local_irq_enable(); + /* + * Service IRQs here before vtime_account_guest_exit() so any + * ticks that occurred while running the guest are accounted to + * the guest. If vtime accounting is enabled, accounting uses + * TB rather than ticks, so it can be done without enabling + * interrupts here, which has the problem that it accounts + * interrupt processing overhead to the host. + */ + local_irq_disable(); + } + vtime_account_guest_exit(); local_irq_enable(); diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c index b1abcb816439..75381beb7514 100644 --- a/arch/powerpc/kvm/booke.c +++ b/arch/powerpc/kvm/booke.c @@ -1016,7 +1016,21 @@ int kvmppc_handle_exit(struct kvm_vcpu *vcpu, unsigned int exit_nr) } trace_kvm_exit(exit_nr, vcpu); - guest_exit_irqoff(); + + context_tracking_guest_exit(); + if (!vtime_accounting_enabled_this_cpu()) { + local_irq_enable(); + /* + * Service IRQs here before vtime_account_guest_exit() so any + * ticks that occurred while running the guest are accounted to + * the guest. If vtime accounting is enabled, accounting uses + * TB rather than ticks, so it can be done without enabling + * interrupts here, which has the problem that it accounts + * interrupt processing overhead to the host. + */ + local_irq_disable(); + } + vtime_account_guest_exit(); local_irq_enable();