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[v6,03/21] KVM: x86: Take the pvclock sync lock behind the tsc_write_lock

Message ID 20210804085819.846610-4-oupton@google.com (mailing list archive)
State New, archived
Headers show
Series KVM: Add idempotent controls for migrating system counter state | expand

Commit Message

Oliver Upton Aug. 4, 2021, 8:58 a.m. UTC 
A later change requires that the pvclock sync lock be taken while
holding the tsc_write_lock. Change the locking in kvm_synchronize_tsc()
to align with the requirement to isolate the locking change to its own
commit.

Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: Oliver Upton <oupton@google.com>
---
 Documentation/virt/kvm/locking.rst | 11 +++++++++++
 arch/x86/kvm/x86.c                 |  2 +-
 2 files changed, 12 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/locking.rst
index 8138201efb09..0bf346adac2a 100644
--- a/Documentation/virt/kvm/locking.rst
+++ b/Documentation/virt/kvm/locking.rst
@@ -36,6 +36,9 @@  On x86:
   holding kvm->arch.mmu_lock (typically with ``read_lock``, otherwise
   there's no need to take kvm->arch.tdp_mmu_pages_lock at all).
 
+- kvm->arch.tsc_write_lock is taken outside
+  kvm->arch.pvclock_gtod_sync_lock
+
 Everything else is a leaf: no other lock is taken inside the critical
 sections.
 
@@ -222,6 +225,14 @@  time it will be set using the Dirty tracking mechanism described above.
 :Comment:	'raw' because hardware enabling/disabling must be atomic /wrt
 		migration.
 
+:Name:		kvm_arch::pvclock_gtod_sync_lock
+:Type:		raw_spinlock_t
+:Arch:		x86
+:Protects:	kvm_arch::{cur_tsc_generation,cur_tsc_nsec,cur_tsc_write,
+			cur_tsc_offset,nr_vcpus_matched_tsc}
+:Comment:	'raw' because updating the kvm master clock must not be
+		preempted.
+
 :Name:		kvm_arch::tsc_write_lock
 :Type:		raw_spinlock
 :Arch:		x86
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 26f1fa263192..93b449761fbe 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2529,7 +2529,6 @@  static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 data)
 	vcpu->arch.this_tsc_write = kvm->arch.cur_tsc_write;
 
 	kvm_vcpu_write_tsc_offset(vcpu, offset);
-	raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags);
 
 	spin_lock_irqsave(&kvm->arch.pvclock_gtod_sync_lock, flags);
 	if (!matched) {
@@ -2540,6 +2539,7 @@  static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 data)
 
 	kvm_track_tsc_matching(vcpu);
 	spin_unlock_irqrestore(&kvm->arch.pvclock_gtod_sync_lock, flags);
+	raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags);
 }
 
 static inline void adjust_tsc_offset_guest(struct kvm_vcpu *vcpu,