Commit 6b72d057 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

KVM: x86: use again the flush argument of __link_shadow_page() 



Except in the case of parentless nested-TDP pages, mmu_page_zap_pte()
clears the SPTE but leaves the invalid_list empty.  In this case, using
kvm_flush_remote_tlbs() as kvm_mmu_remote_flush_or_zap() does is overkill.
Avoid flushing the entirety of the remote TLBs unless the invalid_list
was populated: instead, use a more efficient gfn-targeting flush (if
available) and skip it altogether if the caller guarantees that a TLB
flush is not necessary.

Based-on: <20260503201029.106481-1-pbonzini@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Message-ID: <20260503210917.121840-1-pbonzini@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 87c81016

arch/x86/kvm/mmu/mmu.c

+21 −2
Original line number Diff line number Diff line
@@ -2526,6 +2526,23 @@ static void shadow_walk_next(struct kvm_shadow_walk_iterator *iterator) 
	__shadow_walk_next(iterator, *iterator->sptep);

}



/*

 * Note: while normally KVM uses a "bool flush" return value to let

 * the caller batch flushes, __link_shadow_page() flushes immediately

 * before populating the parent PTE with the new shadow page.  The

 * typical callers, direct_map() and FNAME(fetch)(), are not going

 * to zap more than one huge SPTE anyway.

 *

 * The only exception, where @flush can be false, is when a huge SPTE

 * is replaced with a shadow page SPTE with a fully populated page table,

 * which can happen from shadow_mmu_split_huge_page().  In this case,

 * no memory is unmapped across the change to the page tables and no

 * immediate flush is needed for correctness.

 *

 * Even in that case, calls to kvm_mmu_commit_zap_page() are not

 * batched.  Doing so would require adding an invalid_list argument

 * all the way down to __walk_slot_rmaps().

 */

static void __link_shadow_page(struct kvm *kvm,

			       struct kvm_mmu_memory_cache *cache, u64 *sptep,

			       struct kvm_mmu_page *sp, bool flush)
@@ -2541,8 +2558,10 @@ static void __link_shadow_page(struct kvm *kvm, 
		parent_sp = sptep_to_sp(sptep);

		WARN_ON_ONCE(parent_sp->role.level == PG_LEVEL_4K);



		mmu_page_zap_pte(kvm, parent_sp, sptep, &invalid_list);

		kvm_mmu_remote_flush_or_zap(kvm, &invalid_list, true);

		if (mmu_page_zap_pte(kvm, parent_sp, sptep, &invalid_list))

			kvm_mmu_commit_zap_page(kvm, &invalid_list);

		else if (flush)

			kvm_flush_remote_tlbs_sptep(kvm, sptep);

	}



	spte = make_nonleaf_spte(sp->spt, sp_ad_disabled(sp));