linux-kernel - [PATCH 4/7] KVM: MMU: document mmio page fault

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Message-Id: <1371632965-20077-5-git-send-email-xiaoguangrong@linux.vnet.ibm.com>
Date:	Wed, 19 Jun 2013 17:09:22 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	gleb@...hat.com
Cc:	avi.kivity@...il.com, mtosatti@...hat.com, pbonzini@...hat.com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Subject: [PATCH 4/7] KVM: MMU: document mmio page fault

Document it to Documentation/virtual/kvm/mmu.txt

Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
---
 Documentation/virtual/kvm/mmu.txt | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/Documentation/virtual/kvm/mmu.txt b/Documentation/virtual/kvm/mmu.txt
index 5a6b2e2..4fb442b 100644
--- a/Documentation/virtual/kvm/mmu.txt
+++ b/Documentation/virtual/kvm/mmu.txt
@@ -270,14 +270,21 @@ This is the most complicated event.  The cause of a page fault can be:
 
 Handling a page fault is performed as follows:
 
+ - if the RSV bit of the error code is set, the page fault is caused by guest
+   accessing MMIO, walk shadow page table to get the last spte where the mmio
+   information is stored and cache the information to vcpu->arch.mmio_gva,
+   vcpu->arch.access and vcpu->arch.mmio_gfn then call the emulator to emulate
+   the instruction who will get the benefit from the cached mmio info
  - if needed, walk the guest page tables to determine the guest translation
    (gva->gpa or ngpa->gpa)
    - if permissions are insufficient, reflect the fault back to the guest
  - determine the host page
-   - if this is an mmio request, there is no host page; call the emulator
-     to emulate the instruction instead
+   - if this is an mmio request, there is no host page; cache the info to
+     vcpu->arch.mmio_gva, vcpu->arch.access and vcpu->arch.mmio_gfn
  - walk the shadow page table to find the spte for the translation,
    instantiating missing intermediate page tables as necessary
+   - If this is an mmio request, cache the mmio info to the spte and set some
+     reserved bits on the spte
  - try to unsynchronize the page
    - if successful, we can let the guest continue and modify the gpte
  - emulate the instruction
-- 
1.8.1.4

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