linux-toradex.git/arch/x86/kvm/mmu.h, branch v3.7.9

KVM: MMU: Optimize is_last_gpte()

2012-09-20T10:00:09+00:00

Instead of branchy code depending on level, gpte.ps, and mmu configuration,
prepare everything in a bitmap during mode changes and look it up during
runtime.

Reviewed-by: Xiao Guangrong 
Signed-off-by: Avi Kivity

KVM: MMU: Optimize pte permission checks

2012-09-20T10:00:08+00:00

walk_addr_generic() permission checks are a maze of branchy code, which is
performed four times per lookup.  It depends on the type of access, efer.nxe,
cr0.wp, cr4.smep, and in the near future, cr4.smap.

Optimize this away by precalculating all variants and storing them in a
bitmap.  The bitmap is recalculated when rarely-changing variables change
(cr0, cr4) and is indexed by the often-changing variables (page fault error
code, pte access permissions).

The permission check is moved to the end of the loop, otherwise an SMEP
fault could be reported as a false positive, when PDE.U=1 but PTE.U=0.
Noted by Xiao Guangrong.

The result is short, branch-free code.

Reviewed-by: Xiao Guangrong 
Signed-off-by: Avi Kivity

KVM: MMU: Push clean gpte write protection out of gpte_access()

2012-09-20T10:00:07+00:00

gpte_access() computes the access permissions of a guest pte and also
write-protects clean gptes.  This is wrong when we are servicing a
write fault (since we'll be setting the dirty bit momentarily) but
correct when instantiating a speculative spte, or when servicing a
read fault (since we'll want to trap a following write in order to
set the dirty bit).

It doesn't seem to hurt in practice, but in order to make the code
readable, push the write protection out of gpte_access() and into
a new protect_clean_gpte() which is called explicitly when needed.

Reviewed-by: Xiao Guangrong 
Signed-off-by: Avi Kivity

KVM: MMU: mmio page fault support

2011-07-24T08:50:40+00:00

The idea is from Avi:

| We could cache the result of a miss in an spte by using a reserved bit, and
| checking the page fault error code (or seeing if we get an ept violation or
| ept misconfiguration), so if we get repeated mmio on a page, we don't need to
| search the slot list/tree.
| (https://lkml.org/lkml/2011/2/22/221)

When the page fault is caused by mmio, we cache the info in the shadow page
table, and also set the reserved bits in the shadow page table, so if the mmio
is caused again, we can quickly identify it and emulate it directly

Searching mmio gfn in memslots is heavy since we need to walk all memeslots, it
can be reduced by this feature, and also avoid walking guest page table for
soft mmu.

[jan: fix operator precedence issue]

Signed-off-by: Xiao Guangrong 
Signed-off-by: Jan Kiszka 
Signed-off-by: Avi Kivity

KVM: MMU: cache mmio info on page fault path

2011-07-24T08:50:26+00:00

If the page fault is caused by mmio, we can cache the mmio info, later, we do
not need to walk guest page table and quickly know it is a mmio fault while we
emulate the mmio instruction

Signed-off-by: Xiao Guangrong 
Signed-off-by: Avi Kivity

KVM: MMU: Don't track nested fault info in error-code

2010-10-24T08:52:55+00:00

This patch moves the detection whether a page-fault was
nested or not out of the error code and moves it into a
separate variable in the fault struct.

Signed-off-by: Joerg Roedel 
Signed-off-by: Avi Kivity

KVM: MMU: Introduce init_kvm_nested_mmu()

2010-10-24T08:52:39+00:00

This patch introduces the init_kvm_nested_mmu() function
which is used to re-initialize the nested mmu when the l2
guest changes its paging mode.

Signed-off-by: Joerg Roedel 
Signed-off-by: Avi Kivity

KVM: MMU: Introduce kvm_init_shadow_mmu helper function

2010-10-24T08:52:32+00:00

Some logic of the init_kvm_softmmu function is required to
build the Nested Nested Paging context. So factor the
required logic into a seperate function and export it.
Also make the whole init path suitable for more than one mmu
context.

Signed-off-by: Joerg Roedel 
Signed-off-by: Avi Kivity

KVM: replace x86 kvm n_free_mmu_pages with n_used_mmu_pages

2010-10-24T08:51:18+00:00

Doing this makes the code much more readable.  That's
borne out by the fact that this patch removes code.  "used"
also happens to be the number that we need to return back to
the slab code when our shrinker gets called.  Keeping this
value as opposed to free makes the next patch simpler.

So, 'struct kvm' is kzalloc()'d.  'struct kvm_arch' is a
structure member (and not a pointer) of 'struct kvm'.  That
means they start out zeroed.  I _think_ they get initialized
properly by kvm_mmu_change_mmu_pages().  But, that only happens
via kvm ioctls.

Another benefit of storing 'used' intead of 'free' is
that the values are consistent from the moment the structure is
allocated: no negative "used" value.

Signed-off-by: Dave Hansen 
Signed-off-by: Tim Pepper 
Signed-off-by: Avi Kivity

KVM: abstract kvm x86 mmu->n_free_mmu_pages

2010-10-24T08:51:17+00:00

"free" is a poor name for this value.  In this context, it means,
"the number of mmu pages which this kvm instance should be able to
allocate."  But "free" implies much more that the objects are there
and ready for use.  "available" is a much better description, especially
when you see how it is calculated.

In this patch, we abstract its use into a function.  We'll soon
replace the function's contents by calculating the value in a
different way.

All of the reads of n_free_mmu_pages are taken care of in this
patch.  The modification sites will be handled in a patch
later in the series.

Signed-off-by: Dave Hansen 
Signed-off-by: Tim Pepper 
Signed-off-by: Avi Kivity