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>

2 files changed, 0 insertions, 33 deletions

diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h
index 2d62f7b0d377..69305441f40d 100644
--- a/arch/loongarch/include/asm/kvm_host.h
+++ b/arch/loongarch/include/asm/kvm_host.h
@@ -203,7 +203,6 @@ void kvm_flush_tlb_all(void);
 void kvm_flush_tlb_gpa(struct kvm_vcpu *vcpu, unsigned long gpa);
 int kvm_handle_mm_fault(struct kvm_vcpu *vcpu, unsigned long badv, bool write);
 
-void kvm_set_spte_hva(struct kvm *kvm, unsigned long hva, pte_t pte);
 int kvm_unmap_hva_range(struct kvm *kvm, unsigned long start, unsigned long end, bool blockable);
 int kvm_age_hva(struct kvm *kvm, unsigned long start, unsigned long end);
 int kvm_test_age_hva(struct kvm *kvm, unsigned long hva);
diff --git a/arch/loongarch/kvm/mmu.c b/arch/loongarch/kvm/mmu.c
index a556cff35740..98883aa23ab8 100644
--- a/arch/loongarch/kvm/mmu.c
+++ b/arch/loongarch/kvm/mmu.c
@@ -494,38 +494,6 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 			range->end << PAGE_SHIFT, &ctx);
 }
 
-bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
-{
-	unsigned long prot_bits;
-	kvm_pte_t *ptep;
-	kvm_pfn_t pfn = pte_pfn(range->arg.pte);
-	gpa_t gpa = range->start << PAGE_SHIFT;
-
-	ptep = kvm_populate_gpa(kvm, NULL, gpa, 0);
-	if (!ptep)
-		return false;
-
-	/* Replacing an absent or old page doesn't need flushes */
-	if (!kvm_pte_present(NULL, ptep) || !kvm_pte_young(*ptep)) {
-		kvm_set_pte(ptep, 0);
-		return false;
-	}
-
-	/* Fill new pte if write protected or page migrated */
-	prot_bits = _PAGE_PRESENT | __READABLE;
-	prot_bits |= _CACHE_MASK & pte_val(range->arg.pte);
-
-	/*
-	 * Set _PAGE_WRITE or _PAGE_DIRTY iff old and new pte both support
-	 * _PAGE_WRITE for map_page_fast if next page write fault
-	 * _PAGE_DIRTY since gpa has already recorded as dirty page
-	 */
-	prot_bits |= __WRITEABLE & *ptep & pte_val(range->arg.pte);
-	kvm_set_pte(ptep, kvm_pfn_pte(pfn, __pgprot(prot_bits)));
-
-	return true;
-}
-
 bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	kvm_ptw_ctx ctx;