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Documentation: KVM: make corrections to locking.rst

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Correct grammar and punctuation.
Use "read-only" for consistency.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20230612030810.23376-3-rdunlap@infradead.org
This commit is contained in:
Randy Dunlap 2023-06-11 20:08:08 -07:00 • committed by Jonathan Corbet
parent 4c60d49913
commit c37fa9dbb7
1 changed files with 9 additions and 9 deletions
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18
Documentation/virt/kvm/locking.rst
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@ -67,7 +67,7 @@ following two cases:
2. Write-Protection: The SPTE is present and the fault is caused by
write-protect. That means we just need to change the W bit of the spte.
What we use to avoid all the race is the Host-writable bit and MMU-writable bit
What we use to avoid all the races is the Host-writable bit and MMU-writable bit
on the spte:
- Host-writable means the gfn is writable in the host kernel page tables and in
@ -130,7 +130,7 @@ to gfn. For indirect sp, we disabled fast page fault for simplicity.
A solution for indirect sp could be to pin the gfn, for example via
kvm_vcpu_gfn_to_pfn_atomic, before the cmpxchg. After the pinning:
- We have held the refcount of pfn that means the pfn can not be freed and
- 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 and therefore it cannot be shared between different gfns
by KSM.
@ -186,22 +186,22 @@ writable between reading spte and updating spte. Like below case:
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,
if it can be updated out of mmu-lock [see spte_has_volatile_bits()]; it means
the spte is always atomically 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,
If the spte is updated from writable to read-only, 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
fast page fault path. In order to easily audit the path, we see if TLBs needing
to be flushed caused 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
atomically update the spte, the race caused by fast page fault can be avoided,
atomically update the spte and the race caused by fast page fault can be avoided.
See the comments in spte_has_volatile_bits() and mmu_spte_update().
Lockless Access Tracking:
@ -283,9 +283,9 @@ time it will be set using the Dirty tracking mechanism described above.
:Arch: x86
:Protects: wakeup_vcpus_on_cpu
:Comment: This is a per-CPU lock and it is used for VT-d posted-interrupts.
When VT-d posted-interrupts is supported and the VM has assigned
When VT-d posted-interrupts are supported and the VM has assigned
devices, we put the blocked vCPU on the list blocked_vcpu_on_cpu
protected by blocked_vcpu_on_cpu_lock, when VT-d hardware issues
protected by blocked_vcpu_on_cpu_lock. When VT-d hardware issues
wakeup notification event since external interrupts from the
assigned devices happens, we will find the vCPU on the list to
wakeup.