From: Mauro Carvalho Chehab <mchehab@infradead.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Cornelia Huck <cohuck@redhat.com>,
Linux Media Mailing List <linux-media@vger.kernel.org>,
Jonathan Corbet <corbet@lwn.net>,
kvm@vger.kernel.org, linux-doc@vger.kernel.org
Subject: Re: [PATCH v2 21/27] docs: kvm: Convert locking.txt to ReST format
Date: Fri, 7 Feb 2020 07:24:09 +0100 [thread overview]
Message-ID: <20200207072409.2cb038da@infradead.org> (raw)
In-Reply-To: <20200206234736.196ef417@kernel.org>
>
> >
> > Would be nicer but this is acceptable too I think. Especially, the
> > monospaced font allows breaking the table and keeping the parts aligned.
I couldn't resist trying to use a table ;-)
The following patch does that. IMO, it looks nice on both text and html
outputs.
Cheers,
Mauro
diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/locking.rst
index 428cb3412ecc..c02291beac3f 100644
--- a/Documentation/virt/kvm/locking.rst
+++ b/Documentation/virt/kvm/locking.rst
@@ -59,30 +59,39 @@ The mapping from gfn to pfn may be changed since we can only ensure the pfn
is not changed during cmpxchg. This is a ABA problem, for example, below case
will happen:
-At the beginning::
-
- gpte = gfn1
- gfn1 is mapped to pfn1 on host
- spte is the shadow page table entry corresponding with gpte and
- spte = pfn1
-
- VCPU 0 VCPU0
-
-on fast page fault path::
-
- old_spte = *spte;
- pfn1 is swapped out:
- spte = 0;
-
- pfn1 is re-alloced for gfn2.
-
- gpte is changed to point to
- gfn2 by the guest:
- spte = pfn1;
-
- if (cmpxchg(spte, old_spte, old_spte+W)
- mark_page_dirty(vcpu->kvm, gfn1)
- OOPS!!!
++------------------------------------------------------------------------+
+| At the beginning:: |
+| |
+| gpte = gfn1 |
+| gfn1 is mapped to pfn1 on host |
+| spte is the shadow page table entry corresponding with gpte and |
+| spte = pfn1 |
++------------------------------------------------------------------------+
+| On fast page fault path: |
++------------------------------------+-----------------------------------+
+| CPU 0: | CPU 1: |
++------------------------------------+-----------------------------------+
+| :: | |
+| | |
+| old_spte = *spte; | |
++------------------------------------+-----------------------------------+
+| | pfn1 is swapped out:: |
+| | |
+| | spte = 0; |
+| | |
+| | pfn1 is re-alloced for gfn2. |
+| | |
+| | gpte is changed to point to |
+| | gfn2 by the guest:: |
+| | |
+| | spte = pfn1; |
++------------------------------------+-----------------------------------+
+| :: |
+| |
+| if (cmpxchg(spte, old_spte, old_spte+W) |
+| mark_page_dirty(vcpu->kvm, gfn1) |
+| OOPS!!! |
++------------------------------------------------------------------------+
We dirty-log for gfn1, that means gfn2 is lost in dirty-bitmap.
@@ -109,36 +118,42 @@ Accessed bit and Dirty bit can not be lost.
But it is not true after fast page fault since the spte can be marked
writable between reading spte and updating spte. Like below case:
-At the beginning::
-
- spte.W = 0
- spte.Accessed = 1
-
- VCPU 0 VCPU0
-
-In mmu_spte_clear_track_bits()::
-
- old_spte = *spte;
-
- /* 'if' condition is satisfied. */
- if (old_spte.Accessed == 1 &&
- old_spte.W == 0)
- spte = 0ull;
- on fast page fault path:
- spte.W = 1
- memory write on the spte:
- spte.Dirty = 1
-
-
- else
- old_spte = xchg(spte, 0ull)
-
-
- if (old_spte.Accessed == 1)
- kvm_set_pfn_accessed(spte.pfn);
- if (old_spte.Dirty == 1)
- kvm_set_pfn_dirty(spte.pfn);
- OOPS!!!
++------------------------------------------------------------------------+
+| At the beginning:: |
+| |
+| spte.W = 0 |
+| spte.Accessed = 1 |
++------------------------------------+-----------------------------------+
+| CPU 0: | CPU 1: |
++------------------------------------+-----------------------------------+
+| In mmu_spte_clear_track_bits():: | |
+| | |
+| old_spte = *spte; | |
+| | |
+| | |
+| /* 'if' condition is satisfied. */| |
+| if (old_spte.Accessed == 1 && | |
+| old_spte.W == 0) | |
+| spte = 0ull; | |
++------------------------------------+-----------------------------------+
+| | on fast page fault path:: |
+| | |
+| | spte.W = 1 |
+| | |
+| | memory write on the spte:: |
+| | |
+| | spte.Dirty = 1 |
++------------------------------------+-----------------------------------+
+| :: | |
+| | |
+| else | |
+| old_spte = xchg(spte, 0ull) | |
+| if (old_spte.Accessed == 1) | |
+| kvm_set_pfn_accessed(spte.pfn);| |
+| if (old_spte.Dirty == 1) | |
+| kvm_set_pfn_dirty(spte.pfn); | |
+| OOPS!!! | |
++------------------------------------+-----------------------------------+
The Dirty bit is lost in this case.
next prev parent reply other threads:[~2020-02-07 6:24 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-06 14:49 [PATCH v2 00/27] docs: virt: manually convert text documents to ReST format Mauro Carvalho Chehab
2020-02-06 14:49 ` [PATCH v2 01/27] docs: kvm: add arm/pvtime.rst to index.rst Mauro Carvalho Chehab
2020-02-06 14:49 ` [PATCH v2 02/27] docs: virt: convert UML documentation to ReST Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 03/27] docs: virt: user_mode_linux.rst: update compiling instructions Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 04/27] docs: virt: user_mode_linux.rst: fix URL references Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 05/27] docs: virt: convert halt-polling.txt to ReST format Mauro Carvalho Chehab
2020-02-06 15:41 ` Cornelia Huck
2020-02-06 14:50 ` [PATCH v2 06/27] docs: virt: Convert msr.txt " Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 07/27] docs: kvm: devices/arm-vgic-its.txt " Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 08/27] docs: kvm: devices/arm-vgit-v3.txt to ReST Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 09/27] docs: kvm: convert devices/arm-vgit.txt " Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 10/27] docs: kvm: convert devices/mpic.txt " Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 11/27] docs: kvm: convert devices/s390_flic.txt " Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 12/27] docs: kvm: convert devices/vcpu.txt " Mauro Carvalho Chehab
2020-02-06 15:47 ` Cornelia Huck
2020-02-06 14:50 ` [PATCH v2 13/27] " Mauro Carvalho Chehab
2020-02-06 15:54 ` Cornelia Huck
2020-02-06 14:50 ` [PATCH v2 14/27] docs: kvm: convert devices/vm.txt " Mauro Carvalho Chehab
2020-02-06 15:57 ` Cornelia Huck
2020-02-06 14:50 ` [PATCH v2 15/27] docs: kvm: convert devices/xics.txt " Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 16/27] docs: kvm: convert devices/xive.txt " Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 17/27] docs: kvm: Convert api.txt to ReST format Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 18/27] docs: kvm: convert arm/hyp-abi.txt to ReST Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 19/27] docs: kvm: arm/psci.txt: convert " Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 20/27] docs: kvm: Convert hypercalls.txt to ReST format Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 21/27] docs: kvm: Convert locking.txt " Mauro Carvalho Chehab
2020-02-06 16:11 ` Cornelia Huck
2020-02-06 21:57 ` Paolo Bonzini
2020-02-06 22:47 ` Mauro Carvalho Chehab
2020-02-06 23:13 ` Paolo Bonzini
2020-02-07 6:24 ` Mauro Carvalho Chehab [this message]
2020-02-07 8:48 ` Cornelia Huck
2020-02-10 5:58 ` Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 22/27] docs: kvm: Convert mmu.txt " Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 23/27] docs: kvm: Convert nested-vmx.txt " Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 24/27] docs: kvm: Convert ppc-pv.txt " Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 25/27] docs: kvm: Convert s390-diag.txt " Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 26/27] docs: kvm: Convert timekeeping.txt " Mauro Carvalho Chehab
2020-02-06 14:50 ` [PATCH v2 27/27] docs: kvm: review-checklist.txt: rename to ReST Mauro Carvalho Chehab
2020-02-06 16:13 ` Cornelia Huck
2020-02-06 15:18 ` [PATCH v2 00/27] docs: virt: manually convert text documents to ReST format Paolo Bonzini
2020-02-06 16:17 ` Cornelia Huck
2020-02-06 16:21 ` Mauro Carvalho Chehab
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