KVM: MIPS/MMU: Invalidate stale GVA PTEs on TLBW

Implement invalidation of specific pairs of GVA page table entries in
one or both of the GVA page tables. This is used when existing mappings
are replaced in the guest TLB by emulated TLBWI/TLBWR instructions. Due
to the sharing of page tables in the host kernel range, we should be
careful not to allow host pages to be invalidated.

Add a helper kvm_mips_walk_pgd() which can be used when walking of
either GPA (future patches) or GVA page tables is needed, optionally
with allocation of page tables along the way when they don't exist.

GPA page table walking will need to be protected by the kvm->mmu_lock,
so we also add a small MMU page cache in each KVM VCPU, like that found
for other architectures but smaller. This allows enough pages to be
pre-allocated to handle a single fault without holding the lock,
allowing the helper to run with the lock held without having to handle
allocation failures.

Using the same mechanism for GVA allows the same code to be used, and
allows it to use the same cache of allocated pages if the GPA walk
didn't need to allocate any new tables.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/mips/kvm/emulate.c b/arch/mips/kvm/emulate.c
index 1d399396e486..19eaeda6975c 100644
--- a/arch/mips/kvm/emulate.c
+++ b/arch/mips/kvm/emulate.c
@@ -864,11 +864,17 @@ static void kvm_mips_invalidate_guest_tlb(struct kvm_vcpu *vcpu,
 	/* No need to flush for entries which are already invalid */
 	if (!((tlb->tlb_lo[0] | tlb->tlb_lo[1]) & ENTRYLO_V))
 		return;
+	/* Don't touch host kernel page tables or TLB mappings */
+	if ((unsigned long)tlb->tlb_hi > 0x7fffffff)
+		return;
 	/* User address space doesn't need flushing for KSeg2/3 changes */
 	user = tlb->tlb_hi < KVM_GUEST_KSEG0;
 
 	preempt_disable();
 
+	/* Invalidate page table entries */
+	kvm_trap_emul_invalidate_gva(vcpu, tlb->tlb_hi & VPN2_MASK, user);
+
 	/*
 	 * Probe the shadow host TLB for the entry being overwritten, if one
 	 * matches, invalidate it