Subject: Re: [PATCH v5 5/6] KVM: arm64: Move I-cache flush to the fault handlers

From: Quentin Perret <[email-masked]>
Date: Wed, 2 Jun 2021 10:58:28 +0000

On Thursday 15 Apr 2021 at 19:50:31 (+0800), Yanan Wang wrote:
> In this patch, we move invalidation of I-cache to the fault handlers to

Nit: please avoid using 'This patch' in commit messages, see
Documentation/process/submitting-patches.rst.

> avoid unnecessary I-cache maintenances. On the map path, invalidate the
> I-cache if we are going to create an executable stage-2 mapping for guest.
> And on the permission path, invalidate the I-cache if we are going to add
> an executable permission to the existing guest stage-2 mapping.
> 
> Signed-off-by: Yanan Wang <[email-masked]>
> ---
>  arch/arm64/include/asm/kvm_mmu.h | 15 --------------
>  arch/arm64/kvm/hyp/pgtable.c     | 35 +++++++++++++++++++++++++++++++-
>  arch/arm64/kvm/mmu.c             |  9 +-------
>  3 files changed, 35 insertions(+), 24 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index e9b163c5f023..155492fe5b15 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -187,21 +187,6 @@ static inline bool vcpu_has_cache_enabled(struct kvm_vcpu *vcpu)
>  	return (vcpu_read_sys_reg(vcpu, SCTLR_EL1) & 0b101) == 0b101;
>  }
>  
> -static inline void __invalidate_icache_guest_page(kvm_pfn_t pfn,
> -						  unsigned long size)
> -{
> -	if (icache_is_aliasing()) {
> -		/* any kind of VIPT cache */
> -		__flush_icache_all();
> -	} else if (is_kernel_in_hyp_mode() || !icache_is_vpipt()) {
> -		/* PIPT or VPIPT at EL2 (see comment in __kvm_tlb_flush_vmid_ipa) */
> -		void *va = page_address(pfn_to_page(pfn));
> -
> -		invalidate_icache_range((unsigned long)va,
> -					(unsigned long)va + size);
> -	}
> -}
> -
>  void kvm_set_way_flush(struct kvm_vcpu *vcpu);
>  void kvm_toggle_cache(struct kvm_vcpu *vcpu, bool was_enabled);
>  
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index b480f6d1171e..9f4429d80df0 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -568,6 +568,26 @@ static bool stage2_pte_cacheable(struct kvm_pgtable *pgt, kvm_pte_t pte)
>  	return memattr == KVM_S2_MEMATTR(pgt, NORMAL);
>  }
>  
> +static bool stage2_pte_executable(kvm_pte_t pte)
> +{
> +	return !(pte & KVM_PTE_LEAF_ATTR_HI_S2_XN);
> +}
> +
> +static void stage2_invalidate_icache(void *addr, u64 size)
> +{
> +	if (icache_is_aliasing()) {
> +		/* Any kind of VIPT cache */
> +		__flush_icache_all();
> +	} else if (is_kernel_in_hyp_mode() || !icache_is_vpipt()) {

> +		/*
> +		 * See comment in __kvm_tlb_flush_vmid_ipa().
> +		 * Invalidate PIPT, or VPIPT at EL2.
> +		 */
> +		invalidate_icache_range((unsigned long)addr,
> +					(unsigned long)addr + size);
> +	}
> +}
> +
>  static void stage2_put_pte(kvm_pte_t *ptep, struct kvm_s2_mmu *mmu, u64 addr,
>  			   u32 level, struct kvm_pgtable_mm_ops *mm_ops)
>  {
> @@ -618,6 +638,10 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
>  		if (stage2_pte_cacheable(pgt, new) && !stage2_has_fwb(pgt))
>  			__flush_dcache_area(mm_ops->phys_to_virt(phys),
>  					    granule);
> +
> +		if (stage2_pte_executable(new))
> +			stage2_invalidate_icache(mm_ops->phys_to_virt(phys),
> +						 granule);
>  	}
>  
>  	smp_store_release(ptep, new);
> @@ -896,8 +920,17 @@ static int stage2_attr_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
>  	 * but worst-case the access flag update gets lost and will be
>  	 * set on the next access instead.
>  	 */
> -	if (data->pte != pte)
> +	if (data->pte != pte) {
> +		/*
> +		 * Invalidate the instruction cache before updating
> +		 * if we are going to add the executable permission
> +		 * for the guest stage-2 PTE.
> +		 */
> +		if (!stage2_pte_executable(*ptep) && stage2_pte_executable(pte))
> +			stage2_invalidate_icache(kvm_pte_follow(pte, data->mm_ops),
> +						 kvm_granule_size(level));
>  		WRITE_ONCE(*ptep, pte);
> +	}

As for the dcache stuff, it seems like this would be best placed in an
optional mm_ops callback, and have the kernel implement it.

Thanks,
Quentin

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