4 files changed, 196 insertions, 3 deletions

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 2c9948379469..bf33aaa4c59f 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1946,6 +1946,40 @@ the guest using the specified gsi pin.  The irqfd is removed using
 the KVM_IRQFD_FLAG_DEASSIGN flag, specifying both kvm_irqfd.fd
 and kvm_irqfd.gsi.
 
+4.76 KVM_PPC_ALLOCATE_HTAB
+
+Capability: KVM_CAP_PPC_ALLOC_HTAB
+Architectures: powerpc
+Type: vm ioctl
+Parameters: Pointer to u32 containing hash table order (in/out)
+Returns: 0 on success, -1 on error
+
+This requests the host kernel to allocate an MMU hash table for a
+guest using the PAPR paravirtualization interface.  This only does
+anything if the kernel is configured to use the Book 3S HV style of
+virtualization.  Otherwise the capability doesn't exist and the ioctl
+returns an ENOTTY error.  The rest of this description assumes Book 3S
+HV.
+
+There must be no vcpus running when this ioctl is called; if there
+are, it will do nothing and return an EBUSY error.
+
+The parameter is a pointer to a 32-bit unsigned integer variable
+containing the order (log base 2) of the desired size of the hash
+table, which must be between 18 and 46.  On successful return from the
+ioctl, it will have been updated with the order of the hash table that
+was allocated.
+
+If no hash table has been allocated when any vcpu is asked to run
+(with the KVM_RUN ioctl), the host kernel will allocate a
+default-sized hash table (16 MB).
+
+If this ioctl is called when a hash table has already been allocated,
+the kernel will clear out the existing hash table (zero all HPTEs) and
+return the hash table order in the parameter.  (If the guest is using
+the virtualized real-mode area (VRMA) facility, the kernel will
+re-create the VMRA HPTEs on the next KVM_RUN of any vcpu.)
+
 
 5. The kvm_run structure
 ------------------------
diff --git a/Documentation/virtual/kvm/locking.txt b/Documentation/virtual/kvm/locking.txt
index 3b4cd3bf5631..41b7ac9884b5 100644
--- a/Documentation/virtual/kvm/locking.txt
+++ b/Documentation/virtual/kvm/locking.txt
@@ -6,7 +6,129 @@ KVM Lock Overview
 
 (to be written)
 
-2. Reference
+2: Exception
+------------
+
+Fast page fault:
+
+Fast page fault is the fast path which fixes the guest page fault out of
+the mmu-lock on x86. Currently, the page fault can be fast only if the
+shadow page table is present and it is caused by write-protect, that means
+we just need change the W bit of the spte.
+
+What we use to avoid all the race is the SPTE_HOST_WRITEABLE bit and
+SPTE_MMU_WRITEABLE bit on the spte:
+- SPTE_HOST_WRITEABLE means the gfn is writable on host.
+- SPTE_MMU_WRITEABLE means the gfn is writable on mmu. The bit is set when
+  the gfn is writable on guest mmu and it is not write-protected by shadow
+  page write-protection.
+
+On fast page fault path, we will use cmpxchg to atomically set the spte W
+bit if spte.SPTE_HOST_WRITEABLE = 1 and spte.SPTE_WRITE_PROTECT = 1, this
+is safe because whenever changing these bits can be detected by cmpxchg.
+
+But we need carefully check these cases:
+1): The mapping from gfn to pfn
+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!!!
+
+We dirty-log for gfn1, that means gfn2 is lost in dirty-bitmap.
+
+For direct sp, we can easily avoid it since the spte of direct sp is fixed
+to gfn. For indirect sp, before we do cmpxchg, we call gfn_to_pfn_atomic()
+to pin gfn to pfn, because after gfn_to_pfn_atomic():
+- We have held the refcount of pfn that means the pfn can not be freed and
+  be reused for another gfn.
+- The pfn is writable that means it can not be shared between different gfns
+  by KSM.
+
+Then, we can ensure the dirty bitmaps is correctly set for a gfn.
+
+Currently, to simplify the whole things, we disable fast page fault for
+indirect shadow page.
+
+2): Dirty bit tracking
+In the origin code, the spte can be fast updated (non-atomically) if the
+spte is read-only and the Accessed bit has already been set since the
+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.Accssed == 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.Accssed == 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.
+
+In order to avoid this kind of issue, we always treat the spte as "volatile"
+if it can be updated out of mmu-lock, see spte_has_volatile_bits(), it means,
+the spte is always atomicly updated in this case.
+
+3): flush tlbs due to spte updated
+If the spte is updated from writable to readonly, we should flush all TLBs,
+otherwise rmap_write_protect will find a read-only spte, even though the
+writable spte might be cached on a CPU's TLB.
+
+As mentioned before, the spte can be updated to writable out of mmu-lock on
+fast page fault path, in order to easily audit the path, we see if TLBs need
+be flushed caused by this reason in mmu_spte_update() since this is a common
+function to update spte (present -> present).
+
+Since the spte is "volatile" if it can be updated out of mmu-lock, we always
+atomicly update the spte, the race caused by fast page fault can be avoided,
+See the comments in spte_has_volatile_bits() and mmu_spte_update().
+
+3. Reference
 ------------
 
 Name:           kvm_lock
@@ -23,3 +145,9 @@ Arch:		x86
 Protects:       - kvm_arch::{last_tsc_write,last_tsc_nsec,last_tsc_offset}
                 - tsc offset in vmcb
 Comment:        'raw' because updating the tsc offsets must not be preempted.
+
+Name:           kvm->mmu_lock
+Type:           spinlock_t
+Arch:           any
+Protects:       -shadow page/shadow tlb entry
+Comment:        it is a spinlock since it is used in mmu notifier.
diff --git a/Documentation/virtual/kvm/msr.txt b/Documentation/virtual/kvm/msr.txt
index 96b41bd97523..730471048583 100644
--- a/Documentation/virtual/kvm/msr.txt
+++ b/Documentation/virtual/kvm/msr.txt
@@ -223,3 +223,36 @@ MSR_KVM_STEAL_TIME: 0x4b564d03
                 steal: the amount of time in which this vCPU did not run, in
                 nanoseconds. Time during which the vcpu is idle, will not be
                 reported as steal time.
+
+MSR_KVM_EOI_EN: 0x4b564d04
+        data: Bit 0 is 1 when PV end of interrupt is enabled on the vcpu; 0
+        when disabled.  Bit 1 is reserved and must be zero.  When PV end of
+        interrupt is enabled (bit 0 set), bits 63-2 hold a 4-byte aligned
+        physical address of a 4 byte memory area which must be in guest RAM and
+        must be zeroed.
+
+        The first, least significant bit of 4 byte memory location will be
+        written to by the hypervisor, typically at the time of interrupt
+        injection.  Value of 1 means that guest can skip writing EOI to the apic
+        (using MSR or MMIO write); instead, it is sufficient to signal
+        EOI by clearing the bit in guest memory - this location will
+        later be polled by the hypervisor.
+        Value of 0 means that the EOI write is required.
+
+        It is always safe for the guest to ignore the optimization and perform
+        the APIC EOI write anyway.
+
+        Hypervisor is guaranteed to only modify this least
+        significant bit while in the current VCPU context, this means that
+        guest does not need to use either lock prefix or memory ordering
+        primitives to synchronise with the hypervisor.
+
+        However, hypervisor can set and clear this memory bit at any time:
+        therefore to make sure hypervisor does not interrupt the
+        guest and clear the least significant bit in the memory area
+        in the window between guest testing it to detect
+        whether it can skip EOI apic write and between guest
+        clearing it to signal EOI to the hypervisor,
+        guest must both read the least significant bit in the memory area and
+        clear it using a single CPU instruction, such as test and clear, or
+        compare and exchange.
diff --git a/Documentation/virtual/kvm/ppc-pv.txt b/Documentation/virtual/kvm/ppc-pv.txt
index 6e7c37050930..4911cf95c67e 100644
--- a/Documentation/virtual/kvm/ppc-pv.txt
+++ b/Documentation/virtual/kvm/ppc-pv.txt
@@ -109,8 +109,6 @@ The following bits are safe to be set inside the guest:
 
   MSR_EE
   MSR_RI
-  MSR_CR
-  MSR_ME
 
 If any other bit changes in the MSR, please still use mtmsr(d).