KVM: delete .change_pte MMU notifier callback

The .change_pte() MMU notifier callback was intended as an
optimization. The original point of it was that KSM could tell KVM to flip
its secondary PTE to a new location without having to first zap it. At
the time there was also an .invalidate_page() callback; both of them were
*not* bracketed by calls to mmu_notifier_invalidate_range_{start,end}(),
and .invalidate_page() also doubled as a fallback implementation of
.change_pte().

Later on, however, both callbacks were changed to occur within an
invalidate_range_start/end() block.

In the case of .change_pte(), commit 6bdb913f0a70 ("mm: wrap calls to
set_pte_at_notify with invalidate_range_start and invalidate_range_end",
2012-10-09) did so to remove the fallback from .invalidate_page() to
.change_pte() and allow sleepable .invalidate_page() hooks.

This however made KVM's usage of the .change_pte() callback completely
moot, because KVM unmaps the sPTEs during .invalidate_range_start()
and therefore .change_pte() has no hope of finding a sPTE to change.
Drop the generic KVM code that dispatches to kvm_set_spte_gfn(), as
well as all the architecture specific implementations.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Anup Patel <anup@brainfault.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Message-ID: <20240405115815.3226315-2-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 0 insertions, 20 deletions

diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
index a9e2fd7245e1..b63650f9b966 100644
--- a/arch/riscv/kvm/mmu.c
+++ b/arch/riscv/kvm/mmu.c
@@ -550,26 +550,6 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 	return false;
 }
 
-bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
-{
-	int ret;
-	kvm_pfn_t pfn = pte_pfn(range->arg.pte);
-
-	if (!kvm->arch.pgd)
-		return false;
-
-	WARN_ON(range->end - range->start != 1);
-
-	ret = gstage_map_page(kvm, NULL, range->start << PAGE_SHIFT,
-			      __pfn_to_phys(pfn), PAGE_SIZE, true, true);
-	if (ret) {
-		kvm_debug("Failed to map G-stage page (error %d)\n", ret);
-		return true;
-	}
-
-	return false;
-}
-
 bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	pte_t *ptep;