Re: [PATCH v2] KVM: x86/MMU: Do not check unsync status for root SP.

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 07/02/21 13:22, Yu Zhang wrote:
In shadow page table, only leaf SPs may be marked as unsync.
And for non-leaf SPs, we use unsync_children to keep the number
of the unsynced children. In kvm_mmu_sync_root(), sp->unsync
shall always be zero for the root SP, , hence no need to check
it. Instead, a warning inside mmu_sync_children() is added, in
case someone incorrectly used it.

Also, clarify the mmu_need_write_protect(), by moving the warning
into kvm_unsync_page().

Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

This should really be more of a Co-developed-by, and there are a couple adjustments that could be made in the commit message. I've queued the patch and I'll fix it up later.

Paolo

---
Changes in V2:
- warnings added based on Sean's suggestion.

  arch/x86/kvm/mmu/mmu.c | 12 +++++++++---
  1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 86af582..c4797a00cc 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1995,6 +1995,12 @@ static void mmu_sync_children(struct kvm_vcpu *vcpu,
  	LIST_HEAD(invalid_list);
  	bool flush = false;
+ /*
+	 * Only 4k SPTEs can directly be made unsync, the parent pages
+	 * should never be unsyc'd.
+	 */
+	WARN_ON_ONCE(sp->unsync);
+
  	while (mmu_unsync_walk(parent, &pages)) {
  		bool protected = false;
@@ -2502,6 +2508,8 @@ int kvm_mmu_unprotect_page(struct kvm *kvm, gfn_t gfn) static void kvm_unsync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
  {
+	WARN_ON(sp->role.level != PG_LEVEL_4K);
+
  	trace_kvm_mmu_unsync_page(sp);
  	++vcpu->kvm->stat.mmu_unsync;
  	sp->unsync = 1;
@@ -2524,7 +2532,6 @@ bool mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
  		if (sp->unsync)
  			continue;
- WARN_ON(sp->role.level != PG_LEVEL_4K);
  		kvm_unsync_page(vcpu, sp);
  	}
@@ -3406,8 +3413,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu)
  		 * mmu_need_write_protect() describe what could go wrong if this
  		 * requirement isn't satisfied.
  		 */
-		if (!smp_load_acquire(&sp->unsync) &&
-		    !smp_load_acquire(&sp->unsync_children))
+		if (!smp_load_acquire(&sp->unsync_children))
  			return;
write_lock(&vcpu->kvm->mmu_lock);





[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]

  Powered by Linux