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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Peter Xu <peterx@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
	Andrew Jones <drjones@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	"Michael S . Tsirkin" <mst@redhat.com>,
	Jason Wang <jasowang@redhat.com>,
	Kevin Tian <kevin.tian@intel.com>
Subject: Re: [PATCH v10 02/14] KVM: Cache as_id in kvm_memory_slot
Date: Tue, 7 Jul 2020 12:56:58 -0700	[thread overview]
Message-ID: <20200707195658.GK20096@linux.intel.com> (raw)
In-Reply-To: <20200707195009.GE88106@xz-x1>

On Tue, Jul 07, 2020 at 03:50:09PM -0400, Peter Xu wrote:
> On Mon, Jul 06, 2020 at 11:17:32PM -0700, Sean Christopherson wrote:
> > On Fri, Jul 03, 2020 at 02:41:22PM -0400, Peter Xu wrote:
> > > On Thu, Jul 02, 2020 at 04:08:49PM -0700, Sean Christopherson wrote:
> > > > This technically needs to set as_id in the deleted memslot.  I highly doubt
> > > > it will ever matter from a functionality perspective, but it'd be confusing
> > > > to encounter a memslot whose as_id did not match that of its owner.
> > > 
> > > Yeah it shouldn't matter because as_id is directly passed in to look up the
> > > pointer of kvm_memslots in kvm_delete_memslot, and memslot->as_id shouldn't be
> > > further referenced.
> > > 
> > > I can add a comment above if this can clarify things a bit:
> > > 
> > > +	u16 as_id; /* cache of as_id; only valid if npages != 0 */
> > 
> > Why not just set it?
> 
> Because the value is useless even if set? :)

It's useless when things go according to plan, but I can see it being useful
if there's a bug that leads to consumption of a deleted memslot.  Maybe not
"useful" so much as "not misleading".
 
> You mean in kvm_delete_memslot(), am I right?

Yes.

> > It's a single line of code, and there's more than one
> > "shouldn't" in the above.
> 
> If you want, I can both set it and add the comment.  Thanks,

Why bother with the comment?  It'd be wrong in the sense that the as_id is
always valid/accurate, even if npages == 0.

  reply	other threads:[~2020-07-07 19:57 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-01 11:59 [PATCH v10 00/14] KVM: Dirty ring interface Peter Xu
2020-06-01 11:59 ` [PATCH v10 01/14] KVM: X86: Change parameter for fast_page_fault tracepoint Peter Xu
2020-06-01 11:59 ` [PATCH v10 02/14] KVM: Cache as_id in kvm_memory_slot Peter Xu
2020-07-02 23:08   ` Sean Christopherson
2020-07-03 18:41     ` Peter Xu
2020-07-07  6:17       ` Sean Christopherson
2020-07-07 19:50         ` Peter Xu
2020-07-07 19:56           ` Sean Christopherson [this message]
2020-07-07 20:15             ` Peter Xu
2020-07-07 20:26               ` Sean Christopherson
2020-07-07 20:38                 ` Peter Xu
2020-06-01 11:59 ` [PATCH v10 03/14] KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR] Peter Xu
2020-07-03  0:05   ` Sean Christopherson
2020-07-03 19:02     ` Peter Xu
2020-06-01 11:59 ` [PATCH v10 04/14] KVM: Pass in kvm pointer into mark_page_dirty_in_slot() Peter Xu
2020-06-01 11:59 ` [PATCH v10 05/14] KVM: X86: Implement ring-based dirty memory tracking Peter Xu
2020-06-01 11:59 ` [PATCH v10 06/14] KVM: Make dirty ring exclusive to dirty bitmap log Peter Xu
2020-06-01 11:59 ` [PATCH v10 07/14] KVM: Don't allocate dirty bitmap if dirty ring is enabled Peter Xu
2020-06-01 11:59 ` [PATCH v10 08/14] KVM: selftests: Always clear dirty bitmap after iteration Peter Xu
2020-06-01 11:59 ` [PATCH v10 09/14] KVM: selftests: Sync uapi/linux/kvm.h to tools/ Peter Xu
2020-06-01 11:59 ` [PATCH v10 10/14] KVM: selftests: Use a single binary for dirty/clear log test Peter Xu
2020-06-01 11:59 ` [PATCH v10 11/14] KVM: selftests: Introduce after_vcpu_run hook for dirty " Peter Xu
2020-06-01 11:59 ` [PATCH v10 12/14] KVM: selftests: Add dirty ring buffer test Peter Xu
2020-06-01 12:05 ` [PATCH v10 13/14] KVM: selftests: Let dirty_log_test async for dirty ring test Peter Xu
2020-06-01 12:05 ` [PATCH v10 14/14] KVM: selftests: Add "-c" parameter to dirty log test Peter Xu

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