arm/kvm: excise redundant cache maintenance (dcadda14) · Commits · 戴 / test

When modifying Stage-2 page tables, we perform cache maintenance to account for non-coherent page table walks. However, this is unnecessary, as page table walks are guaranteed to be coherent in the presence of the virtualization extensions. Per ARM DDI 0406C.c, section B1.7 ("The Virtualization Extensions"), the virtualization extensions mandate the multiprocessing extensions. Per ARM DDI 0406C.c, section B3.10.1 ("General TLB maintenance requirements"), as described in the sub-section titled "TLB maintenance operations and the memory order model", this maintenance is not required in the presence of the multiprocessing extensions. Hence, we need not perform this cache maintenance when modifying Stage-2 entries. This patch removes the logic for performing the redundant maintenance. To ensure visibility and ordering of updates, a dsb(ishst) that was otherwise implicit in the maintenance is folded into kvm_set_pmd() and kvm_set_pte(). Signed-off-by:

Mark Rutland <mark.rutland@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Marc Zyngier <marc.zyngier@arm.com> Cc: kvmarm@lists.cs.columbia.edu Signed-off-by:

Christoffer Dall <christoffer.dall@linaro.org>

arch/arm/include/asm/kvm_mmu.h

+2 −26

Original line number	Diff line number	Diff line
		@@ -63,37 +63,13 @@ void kvm_clear_hyp_idmap(void);
		static inline void kvm_set_pmd(pmd_t *pmd, pmd_t new_pmd)
		{
		*pmd = new_pmd;
		flush_pmd_entry(pmd);
		dsb(ishst);
		}

		static inline void kvm_set_pte(pte_t *pte, pte_t new_pte)
		{
		*pte = new_pte;
		/*
		* flush_pmd_entry just takes a void pointer and cleans the necessary
		* cache entries, so we can reuse the function for ptes.
		*/
		flush_pmd_entry(pte);
		}

		static inline void kvm_clean_pgd(pgd_t *pgd)
		{
		clean_dcache_area(pgd, PTRS_PER_S2_PGD * sizeof(pgd_t));
		}

		static inline void kvm_clean_pmd(pmd_t *pmd)
		{
		clean_dcache_area(pmd, PTRS_PER_PMD * sizeof(pmd_t));
		}

		static inline void kvm_clean_pmd_entry(pmd_t *pmd)
		{
		clean_pmd_entry(pmd);
		}

		static inline void kvm_clean_pte(pte_t *pte)
		{
		clean_pte_table(pte);
		dsb(ishst);
		}

		static inline pte_t kvm_s2pte_mkwrite(pte_t pte)

arch/arm/kvm/mmu.c

+0 −2

Original line number	Diff line number	Diff line
		@@ -744,7 +744,6 @@ int kvm_alloc_stage2_pgd(struct kvm *kvm)
		if (!pgd)
		return -ENOMEM;

		kvm_clean_pgd(pgd);
		kvm->arch.pgd = pgd;
		return 0;
		}
		@@ -936,7 +935,6 @@ static int stage2_set_pte(struct kvm kvm, struct kvm_mmu_memory_cache cache,
		if (!cache)
		return 0; /* ignore calls from kvm_set_spte_hva */
		pte = mmu_memory_cache_alloc(cache);
		kvm_clean_pte(pte);
		pmd_populate_kernel(NULL, pmd, pte);
		get_page(virt_to_page(pmd));
		}

Admin message