On Mon, Aug 16, 2021, Oliver Upton wrote:
> 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@xxxxxxxxxx>
> Signed-off-by: Oliver Upton <oupton@xxxxxxxxxx>
> ---
> Documentation/virt/kvm/locking.rst | 11 +++++++++++
> arch/x86/kvm/x86.c | 2 +-
> 2 files changed, 12 insertions(+), 1 deletion(-)
>
> 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 b1e9a4885be6..f1434cd388b9 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2533,7 +2533,6 @@ 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) {
> @@ -2544,6 +2543,7 @@ 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);
Drop the irqsave/irqrestore in this patch instead of doing so while refactoring
the code in the next patch.
> + raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags);
> }
>
> static inline void adjust_tsc_offset_guest(struct kvm_vcpu *vcpu,
> --
> 2.33.0.rc1.237.g0d66db33f3-goog
>
_______________________________________________
kvmarm mailing list
kvmarm@xxxxxxxxxxxxxxxxxxxxx
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
