133 lines
4.4 KiB
Diff
133 lines
4.4 KiB
Diff
From cb6d2db0c89d3470b6f10bf77011bd2b33b956d1 Mon Sep 17 00:00:00 2001
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From: Marcelo Tosatti <mtosatti@redhat.com>
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Date: Mon, 17 Apr 2017 12:51:37 -0300
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Subject: [PATCH] KVM: x86: remove irq disablement around
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KVM_SET_CLOCK/KVM_GET_CLOCK
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The disablement of interrupts at KVM_SET_CLOCK/KVM_GET_CLOCK
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attempts to disable software suspend from causing "non atomic behaviour" of
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the operation:
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Add a helper function to compute the kernel time and convert nanoseconds
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back to CPU specific cycles. Note that these must not be called in preemptible
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context, as that would mean the kernel could enter software suspend state,
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which would cause non-atomic operation.
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However, assume the kernel can enter software suspend at the following 2 points:
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ktime_get_ts(&ts);
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1.
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hypothetical_ktime_get_ts(&ts)
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monotonic_to_bootbased(&ts);
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2.
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monotonic_to_bootbased() should be correct relative to a ktime_get_ts(&ts)
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performed after point 1 (that is after resuming from software suspend),
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hypothetical_ktime_get_ts()
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Therefore it is also correct for the ktime_get_ts(&ts) before point 1,
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which is
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ktime_get_ts(&ts) = hypothetical_ktime_get_ts(&ts) + time-to-execute-suspend-code
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Note CLOCK_MONOTONIC does not count during suspension.
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So remove the irq disablement, which causes the following warning on
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-RT kernels:
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With this reasoning, and the -RT bug that the irq disablement causes
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(because spin_lock is now a sleeping lock), remove the IRQ protection as it
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causes:
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[ 1064.668109] in_atomic(): 0, irqs_disabled(): 1, pid: 15296, name:m
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[ 1064.668110] INFO: lockdep is turned off.
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[ 1064.668110] irq event stamp: 0
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[ 1064.668112] hardirqs last enabled at (0): [< (null)>] )
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[ 1064.668116] hardirqs last disabled at (0): [] c0
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[ 1064.668118] softirqs last enabled at (0): [] c0
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[ 1064.668118] softirqs last disabled at (0): [< (null)>] )
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[ 1064.668121] CPU: 13 PID: 15296 Comm: qemu-kvm Not tainted 3.10.0-1
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[ 1064.668121] Hardware name: Dell Inc. PowerEdge R730/0H21J3, BIOS 5
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[ 1064.668123] ffff8c1796b88000 00000000afe7344c ffff8c179abf3c68 f3
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[ 1064.668125] ffff8c179abf3c90 ffffffff930ccb3d ffff8c1b992b3610 f0
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[ 1064.668126] 00007ffc1a26fbc0 ffff8c179abf3cb0 ffffffff9375f694 f0
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[ 1064.668126] Call Trace:
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[ 1064.668132] [] dump_stack+0x19/0x1b
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[ 1064.668135] [] __might_sleep+0x12d/0x1f0
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[ 1064.668138] [] rt_spin_lock+0x24/0x60
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[ 1064.668155] [] __get_kvmclock_ns+0x36/0x110 [k]
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[ 1064.668159] [] ? futex_wait_queue_me+0x103/0x10
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[ 1064.668171] [] kvm_arch_vm_ioctl+0xa2/0xd70 [k]
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[ 1064.668173] [] ? futex_wait+0x1ac/0x2a0
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v2: notice get_kvmclock_ns with the same problem (Pankaj).
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v3: remove useless helper function (Pankaj).
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Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Signed-off-by: Alex Kozyrev <alex.kozyrev@windriver.com>
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---
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arch/x86/kvm/x86.c | 22 +++-------------------
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1 file changed, 3 insertions(+), 19 deletions(-)
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diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
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index 08257ab..8babcb5 100644
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--- a/arch/x86/kvm/x86.c
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+++ b/arch/x86/kvm/x86.c
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@@ -1739,7 +1739,7 @@ static void kvm_gen_update_masterclock(struct kvm *kvm)
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#endif
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}
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-static u64 __get_kvmclock_ns(struct kvm *kvm)
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+u64 get_kvmclock_ns(struct kvm *kvm)
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{
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struct kvm_arch *ka = &kvm->arch;
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struct pvclock_vcpu_time_info hv_clock;
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@@ -1759,18 +1759,6 @@ static u64 __get_kvmclock_ns(struct kvm *kvm)
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return __pvclock_read_cycles(&hv_clock, rdtsc());
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}
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-u64 get_kvmclock_ns(struct kvm *kvm)
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-{
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- unsigned long flags;
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- s64 ns;
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-
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- local_irq_save(flags);
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- ns = __get_kvmclock_ns(kvm);
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- local_irq_restore(flags);
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-
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- return ns;
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-}
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-
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static int kvm_guest_time_update(struct kvm_vcpu *v)
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{
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unsigned long flags, this_tsc_khz, tgt_tsc_khz;
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@@ -4064,10 +4052,8 @@ long kvm_arch_vm_ioctl(struct file *filp,
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goto out;
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r = 0;
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- local_irq_disable();
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- now_ns = __get_kvmclock_ns(kvm);
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+ now_ns = get_kvmclock_ns(kvm);
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kvm->arch.kvmclock_offset += user_ns.clock - now_ns;
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- local_irq_enable();
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kvm_gen_update_masterclock(kvm);
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break;
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}
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@@ -4075,11 +4061,9 @@ long kvm_arch_vm_ioctl(struct file *filp,
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struct kvm_clock_data user_ns;
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u64 now_ns;
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- local_irq_disable();
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- now_ns = __get_kvmclock_ns(kvm);
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+ now_ns = get_kvmclock_ns(kvm);
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user_ns.clock = now_ns;
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user_ns.flags = kvm->arch.use_master_clock ? KVM_CLOCK_TSC_STABLE : 0;
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- local_irq_enable();
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memset(&user_ns.pad, 0, sizeof(user_ns.pad));
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r = -EFAULT;
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--
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1.8.3.1
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