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From: Sean Christopherson <seanjc@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Anish Moorthy <amoorthy@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Oliver Upton <oliver.upton@linux.dev>,
	James Houghton <jthoughton@google.com>,
	Ben Gardon <bgardon@google.com>,
	David Matlack <dmatlack@google.com>,
	Ricardo Koller <ricarkol@google.com>,
	Chao Peng <chao.p.peng@linux.intel.com>,
	Axel Rasmussen <axelrasmussen@google.com>,
	kvm@vger.kernel.org, kvmarm@lists.linux.dev
Subject: Re: [PATCH 5/8] kvm: Add cap/kvm_run field for memory fault exits
Date: Wed, 15 Feb 2023 09:07:44 -0800	[thread overview]
Message-ID: <Y+0RYMfw6pHrSLX4@google.com> (raw)
In-Reply-To: <87mt5fz5g6.wl-maz@kernel.org>

On Wed, Feb 15, 2023, Marc Zyngier wrote:
> On Wed, 15 Feb 2023 01:16:11 +0000, Anish Moorthy <amoorthy@google.com> wrote:
> >  8. Other capabilities.
> >  ======================
> >  
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 109b18e2789c4..9352e7f8480fb 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -801,6 +801,9 @@ struct kvm {
> >  	bool vm_bugged;
> >  	bool vm_dead;
> >  
> > +	rwlock_t mem_fault_nowait_lock;
> > +	bool mem_fault_nowait;
> 
> A full-fat rwlock to protect a single bool? What benefits do you
> expect from a rwlock? Why is it preferable to an atomic access, or a
> simple bitop?

There's no need to have any kind off dedicated atomicity.  The only readers are
in vCPU context, just disallow KVM_CAP_MEM_FAULT_NOWAIT after vCPUs are created.

  reply	other threads:[~2023-02-15 17:07 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-02-15  1:16 [PATCH 0/8] Add memory fault exits to avoid slow GUP Anish Moorthy
2023-02-15  1:16 ` [PATCH 1/8] selftests/kvm: Fix bug in how demand_paging_test calculates paging rate Anish Moorthy
2023-02-15  7:27   ` Oliver Upton
2023-02-15 16:44     ` Sean Christopherson
2023-02-15 18:05       ` Anish Moorthy
2023-02-15  1:16 ` [PATCH 2/8] selftests/kvm: Allow many vcpus per UFFD in demand paging test Anish Moorthy
2023-02-15  1:16 ` [PATCH 3/8] selftests/kvm: Switch demand paging uffd readers to epoll Anish Moorthy
2023-02-15  1:16 ` [PATCH 4/8] kvm: Allow hva_pfn_fast to resolve read-only faults Anish Moorthy
2023-02-15  9:01   ` Oliver Upton
2023-02-15 17:03     ` Sean Christopherson
2023-02-15 18:19       ` Anish Moorthy
2023-02-15  1:16 ` [PATCH 5/8] kvm: Add cap/kvm_run field for memory fault exits Anish Moorthy
2023-02-15  8:41   ` Marc Zyngier
2023-02-15 17:07     ` Sean Christopherson [this message]
2023-02-16 18:53     ` Anish Moorthy
2023-02-16 21:38       ` Sean Christopherson
2023-02-17 19:14         ` Anish Moorthy
2023-02-17 20:33           ` Sean Christopherson
2023-02-23  1:16             ` Anish Moorthy
2023-02-23 20:55               ` Sean Christopherson
2023-02-23 23:03                 ` Anish Moorthy
2023-02-24  0:01                   ` Sean Christopherson
2023-02-17 20:47           ` Sean Christopherson
2023-02-15  8:59   ` Oliver Upton
2023-02-15  1:16 ` [PATCH 6/8] kvm/x86: Add mem fault exit on EPT violations Anish Moorthy
2023-02-15 17:23   ` Sean Christopherson
2023-02-16 22:55     ` Peter Xu
2023-02-23  0:35     ` Anish Moorthy
2023-02-23 20:11       ` Sean Christopherson
2023-02-15  1:16 ` [PATCH 7/8] kvm/arm64: Implement KVM_CAP_MEM_FAULT_NOWAIT for arm64 Anish Moorthy
2023-02-15 18:24   ` Oliver Upton
2023-02-15 23:28     ` Anish Moorthy
2023-02-15 23:37       ` Oliver Upton
2023-02-15  1:16 ` [PATCH 8/8] selftests/kvm: Handle mem fault exits in demand paging test Anish Moorthy
2023-02-15  1:46 ` [PATCH 0/8] Add memory fault exits to avoid slow GUP James Houghton

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