From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Peter Xu <peterx@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
"Michael S . Tsirkin" <mst@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Yan Zhao <yan.y.zhao@intel.com>,
"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
Christophe de Dinechin <dinechin@redhat.com>,
Alex Williamson <alex.williamson@redhat.com>,
Jason Wang <jasowang@redhat.com>,
Kevin Tian <kevin.tian@intel.com>,
Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH v7 03/14] KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR]
Date: Mon, 23 Mar 2020 09:55:51 -0700 [thread overview]
Message-ID: <20200323165551.GS28711@linux.intel.com> (raw)
In-Reply-To: <20200323162617.GK127076@xz-x1>
On Mon, Mar 23, 2020 at 12:26:17PM -0400, Peter Xu wrote:
> On Mon, Mar 23, 2020 at 08:42:16AM -0700, Sean Christopherson wrote:
> > > > Regarding the HVA, it's a bit confusing saying that it's guaranteed to be
> > > > valid, and then contradicting that in the second clause. Maybe something
> > > > like this to explain the GPA->HVA is guaranteed to be valid, but the
> > > > HVA->HPA is not.
> > > >
> > > > /*
> > > > * before use. Note, KVM internal memory slots are guaranteed to remain valid
> > > > * and unchanged until the VM is destroyed, i.e. the GPA->HVA translation will
> > > > * not change. However, the HVA is a user address, i.e. its accessibility is
> > > > * not guaranteed, and must be accessed via __copy_{to,from}_user().
> > > > */
> > >
> > > Sure I can switch to this, though note that I still think the GPA->HVA
> > > is not guaranteed logically because the userspace can unmap any HVA it
> > > wants..
> >
> > You're conflating the GPA->HVA translation with the validity of the HVA,
> > i.e. the HVA->HPA and/or HVA->VMA translation/association. GPA->HVA is
> > guaranteed because userspace doesn't have access to the memslot which
> > defines that transation.
>
> Yes I completely agree if you mean the pure mapping of GPA->HVA.
>
> I think it's a matter of how to define the "valid" when you say
> "guaranteed to remain valid", because I don't think the mapping is
> still valid from the most strict sense if e.g. the backing HVA does
> not exist any more for that GPA->HVA mapping, then the memslot won't
> be anything useful.
Yes. That's why my proposed comment is worded to state that the _memslot_
will remain valid. It deliberately avoids mentioning "valid HVA".
next prev parent reply other threads:[~2020-03-23 16:55 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-18 16:37 [PATCH v7 00/14] KVM: Dirty ring interface Peter Xu
2020-03-18 16:37 ` [PATCH v7 01/14] KVM: X86: Change parameter for fast_page_fault tracepoint Peter Xu
2020-03-18 16:37 ` [PATCH v7 02/14] KVM: Cache as_id in kvm_memory_slot Peter Xu
2020-03-18 16:37 ` [PATCH v7 03/14] KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR] Peter Xu
2020-03-21 19:22 ` Sean Christopherson
2020-03-23 14:58 ` Peter Xu
2020-03-23 15:42 ` Sean Christopherson
2020-03-23 16:26 ` Peter Xu
2020-03-23 16:55 ` Sean Christopherson [this message]
2020-03-23 17:13 ` Peter Xu
2020-03-18 16:37 ` [PATCH v7 04/14] KVM: Pass in kvm pointer into mark_page_dirty_in_slot() Peter Xu
2020-03-18 16:37 ` [PATCH v7 05/14] KVM: X86: Implement ring-based dirty memory tracking Peter Xu
2020-03-18 16:37 ` [PATCH v7 06/14] KVM: Make dirty ring exclusive to dirty bitmap log Peter Xu
2020-03-21 19:12 ` Sean Christopherson
2020-03-23 16:16 ` Peter Xu
2020-03-18 16:37 ` [PATCH v7 07/14] KVM: Don't allocate dirty bitmap if dirty ring is enabled Peter Xu
2020-03-18 16:37 ` [PATCH v7 08/14] KVM: selftests: Always clear dirty bitmap after iteration Peter Xu
2020-03-18 16:37 ` [PATCH v7 09/14] KVM: selftests: Sync uapi/linux/kvm.h to tools/ Peter Xu
2020-03-18 16:37 ` [PATCH v7 10/14] KVM: selftests: Use a single binary for dirty/clear log test Peter Xu
2020-03-19 7:44 ` Andrew Jones
2020-03-18 16:37 ` [PATCH v7 11/14] KVM: selftests: Introduce after_vcpu_run hook for dirty " Peter Xu
2020-03-19 7:50 ` Andrew Jones
2020-03-19 16:37 ` Peter Xu
2020-03-18 16:37 ` [PATCH v7 12/14] KVM: selftests: Add dirty ring buffer test Peter Xu
2020-03-19 17:02 ` Peter Xu
2020-03-18 16:37 ` [PATCH v7 13/14] KVM: selftests: Let dirty_log_test async for dirty ring test Peter Xu
2020-03-18 16:37 ` [PATCH v7 14/14] KVM: selftests: Add "-c" parameter to dirty log test Peter Xu
2020-03-19 7:54 ` Andrew Jones
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