Commit Graph

13 Commits

Author SHA1 Message Date
Xiao Guangrong edc90b7dc4 KVM: MMU: fix SMAP virtualization
KVM may turn a user page to a kernel page when kernel writes a readonly
user page if CR0.WP = 1. This shadow page entry will be reused after
SMAP is enabled so that kernel is allowed to access this user page

Fix it by setting SMAP && !CR0.WP into shadow page's role and reset mmu
once CR4.SMAP is updated

Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2015-05-19 20:52:36 +02:00
David Matlack ee3d1570b5 kvm: fix potentially corrupt mmio cache
vcpu exits and memslot mutations can run concurrently as long as the
vcpu does not aquire the slots mutex. Thus it is theoretically possible
for memslots to change underneath a vcpu that is handling an exit.

If we increment the memslot generation number again after
synchronize_srcu_expedited(), vcpus can safely cache memslot generation
without maintaining a single rcu_dereference through an entire vm exit.
And much of the x86/kvm code does not maintain a single rcu_dereference
of the current memslots during each exit.

We can prevent the following case:

   vcpu (CPU 0)                             | thread (CPU 1)
--------------------------------------------+--------------------------
1  vm exit                                  |
2  srcu_read_unlock(&kvm->srcu)             |
3  decide to cache something based on       |
     old memslots                           |
4                                           | change memslots
                                            | (increments generation)
5                                           | synchronize_srcu(&kvm->srcu);
6  retrieve generation # from new memslots  |
7  tag cache with new memslot generation    |
8  srcu_read_unlock(&kvm->srcu)             |
...                                         |
   <action based on cache occurs even       |
    though the caching decision was based   |
    on the old memslots>                    |
...                                         |
   <action *continues* to occur until next  |
    memslot generation change, which may    |
    be never>                               |
                                            |

By incrementing the generation after synchronizing with kvm->srcu readers,
we ensure that the generation retrieved in (6) will become invalid soon
after (8).

Keeping the existing increment is not strictly necessary, but we
do keep it and just move it for consistency from update_memslots to
install_new_memslots.  It invalidates old cached MMIOs immediately,
instead of having to wait for the end of synchronize_srcu_expedited,
which makes the code more clearly correct in case CPU 1 is preempted
right after synchronize_srcu() returns.

To avoid halving the generation space in SPTEs, always presume that the
low bit of the generation is zero when reconstructing a generation number
out of an SPTE.  This effectively disables MMIO caching in SPTEs during
the call to synchronize_srcu_expedited.  Using the low bit this way is
somewhat like a seqcount---where the protected thing is a cache, and
instead of retrying we can simply punt if we observe the low bit to be 1.

Cc: stable@vger.kernel.org
Signed-off-by: David Matlack <dmatlack@google.com>
Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2014-09-03 10:03:41 +02:00
Xiao Guangrong 5a9b3830d4 KVM: MMU: document fast invalidate all mmio sptes
Document it to Documentation/virtual/kvm/mmu.txt

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2013-06-27 14:20:48 +03:00
Xiao Guangrong f6f8adeef5 KVM: MMU: document fast invalidate all pages
Document it to Documentation/virtual/kvm/mmu.txt

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2013-06-27 14:20:47 +03:00
Xiao Guangrong 2d49c47f35 KVM: MMU: document fast page fault
Document fast page fault to Documentation/virtual/kvm/mmu.txt

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2013-06-27 14:20:46 +03:00
Xiao Guangrong 67652ed343 KVM: MMU: document mmio page fault
Document it to Documentation/virtual/kvm/mmu.txt

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2013-06-27 14:20:44 +03:00
Xiao Guangrong 0cbf8e437b KVM: MMU: document write_flooding_count
Document write_flooding_count to Documentation/virtual/kvm/mmu.txt

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2013-06-27 14:20:43 +03:00
Xiao Guangrong accaefe07d KVM: MMU: document clear_spte_count
Document it to Documentation/virtual/kvm/mmu.txt

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2013-06-27 14:20:42 +03:00
Xiao Guangrong 6c806a7332 KVM: MMU: update the documentation for reverse mapping of parent_pte
Update the document to match the current reverse mapping of
parent_pte

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2013-06-19 12:32:21 +02:00
Takuya Yoshikawa e12091ce7b KVM: Remove unused slot_bitmap from kvm_mmu_page
Not needed any more.

Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
2013-01-14 11:13:58 +02:00
Masanari Iida 40e47125e6 Documentation: Fix multiple typo in Documentation
Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2012-03-07 16:08:24 +01:00
Avi Kivity 411c588dfb KVM: MMU: Adjust shadow paging to work when SMEP=1 and CR0.WP=0
When CR0.WP=0, we sometimes map user pages as kernel pages (to allow
the kernel to write to them).  Unfortunately this also allows the kernel
to fetch from these pages, even if CR4.SMEP is set.

Adjust for this by also setting NX on the spte in these circumstances.

Signed-off-by: Avi Kivity <avi@redhat.com>
2011-07-12 13:16:26 +03:00
Rob Landley ed16648eb5 Move kvm, uml, and lguest subdirectories under a common "virtual" directory, I.E:
cd Documentation
  mkdir virtual
  git mv kvm uml lguest virtual

Signed-off-by: Rob Landley <rlandley@parallels.com>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
2011-05-06 09:22:02 -07:00