Thread (30 messages) 30 messages, 11 authors, 2024-06-12

Re: [PATCH 1/4] KVM: delete .change_pte MMU notifier callback

From: Will Deacon <will@kernel.org>
Date: 2024-04-12 10:44:17
Also in: kvm, kvm-riscv, kvmarm, linux-arm-kernel, linux-mips, linux-mm, linux-perf-users, linux-trace-kernel, lkml, loongarch

On Fri, Apr 05, 2024 at 07:58:12AM -0400, Paolo Bonzini wrote:
quoted hunk ↗ jump to hunk
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index dc04bc767865..ff17849be9f4 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1768,40 +1768,6 @@ 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)
-{
-	kvm_pfn_t pfn = pte_pfn(range->arg.pte);
-
-	if (!kvm->arch.mmu.pgt)
-		return false;
-
-	WARN_ON(range->end - range->start != 1);
-
-	/*
-	 * If the page isn't tagged, defer to user_mem_abort() for sanitising
-	 * the MTE tags. The S2 pte should have been unmapped by
-	 * mmu_notifier_invalidate_range_end().
-	 */
-	if (kvm_has_mte(kvm) && !page_mte_tagged(pfn_to_page(pfn)))
-		return false;
-
-	/*
-	 * We've moved a page around, probably through CoW, so let's treat
-	 * it just like a translation fault and the map handler will clean
-	 * the cache to the PoC.
-	 *
-	 * The MMU notifiers will have unmapped a huge PMD before calling
-	 * ->change_pte() (which in turn calls kvm_set_spte_gfn()) and
-	 * therefore we never need to clear out a huge PMD through this
-	 * calling path and a memcache is not required.
-	 */
-	kvm_pgtable_stage2_map(kvm->arch.mmu.pgt, range->start << PAGE_SHIFT,
-			       PAGE_SIZE, __pfn_to_phys(pfn),
-			       KVM_PGTABLE_PROT_R, NULL, 0);
-
-	return false;
-}
-
 bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	u64 size = (range->end - range->start) << PAGE_SHIFT;
Thanks. It's nice to see this code retire:

Acked-by: Will Deacon <will@kernel.org>

Also, if you're in the business of hacking the MMU notifier code, it
would be really great to change the .clear_flush_young() callback so
that the architecture could handle the TLB invalidation. At the moment,
the core KVM code invalidates the whole VMID courtesy of 'flush_on_ret'
being set by kvm_handle_hva_range(), whereas we could do a much
lighter-weight and targetted TLBI in the architecture page-table code
when we actually update the ptes for small ranges.

Will
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