Messages in this thread | | | Subject | Re: [RFC PATCH 1/4] KVM: arm64: Move the clean of dcache to the map handler | From | "wangyanan (Y)" <> | Date | Fri, 26 Feb 2021 23:58:10 +0800 |
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On 2021/2/25 17:55, Marc Zyngier wrote: > Hi Yanan, > > On Mon, 08 Feb 2021 11:22:47 +0000, > Yanan Wang <wangyanan55@huawei.com> wrote: >> We currently uniformly clean dcache in user_mem_abort() before calling the >> fault handlers, if we take a translation fault and the pfn is cacheable. >> But if there are concurrent translation faults on the same page or block, >> clean of dcache for the first time is necessary while the others are not. >> >> By moving clean of dcache to the map handler, we can easily identify the >> conditions where CMOs are really needed and avoid the unnecessary ones. >> As it's a time consuming process to perform CMOs especially when flushing >> a block range, so this solution reduces much load of kvm and improve the >> efficiency of creating mappings. > That's an interesting approach. However, wouldn't it be better to > identify early that there is already something mapped, and return to > the guest ASAP? > > Can you quantify the benefit of this patch alone? > >> Signed-off-by: Yanan Wang <wangyanan55@huawei.com> >> --- >> arch/arm64/include/asm/kvm_mmu.h | 16 -------------- >> arch/arm64/kvm/hyp/pgtable.c | 38 ++++++++++++++++++++------------ >> arch/arm64/kvm/mmu.c | 14 +++--------- >> 3 files changed, 27 insertions(+), 41 deletions(-) >> >> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h >> index e52d82aeadca..4ec9879e82ed 100644 >> --- a/arch/arm64/include/asm/kvm_mmu.h >> +++ b/arch/arm64/include/asm/kvm_mmu.h >> @@ -204,22 +204,6 @@ static inline bool vcpu_has_cache_enabled(struct kvm_vcpu *vcpu) >> return (vcpu_read_sys_reg(vcpu, SCTLR_EL1) & 0b101) == 0b101; >> } >> >> -static inline void __clean_dcache_guest_page(kvm_pfn_t pfn, unsigned long size) >> -{ >> - void *va = page_address(pfn_to_page(pfn)); >> - >> - /* >> - * With FWB, we ensure that the guest always accesses memory using >> - * cacheable attributes, and we don't have to clean to PoC when >> - * faulting in pages. Furthermore, FWB implies IDC, so cleaning to >> - * PoU is not required either in this case. >> - */ >> - if (cpus_have_const_cap(ARM64_HAS_STAGE2_FWB)) >> - return; >> - >> - kvm_flush_dcache_to_poc(va, size); >> -} >> - >> static inline void __invalidate_icache_guest_page(kvm_pfn_t pfn, >> unsigned long size) >> { >> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c >> index 4d177ce1d536..2f4f87021980 100644 >> --- a/arch/arm64/kvm/hyp/pgtable.c >> +++ b/arch/arm64/kvm/hyp/pgtable.c >> @@ -464,6 +464,26 @@ static int stage2_map_set_prot_attr(enum kvm_pgtable_prot prot, >> return 0; >> } >> >> +static bool stage2_pte_cacheable(kvm_pte_t pte) >> +{ >> + u64 memattr = pte & KVM_PTE_LEAF_ATTR_LO_S2_MEMATTR; >> + return memattr == PAGE_S2_MEMATTR(NORMAL); >> +} >> + >> +static void stage2_flush_dcache(void *addr, u64 size) >> +{ >> + /* >> + * With FWB, we ensure that the guest always accesses memory using >> + * cacheable attributes, and we don't have to clean to PoC when >> + * faulting in pages. Furthermore, FWB implies IDC, so cleaning to >> + * PoU is not required either in this case. >> + */ >> + if (cpus_have_const_cap(ARM64_HAS_STAGE2_FWB)) >> + return; >> + >> + __flush_dcache_area(addr, size); >> +} >> + >> static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level, >> kvm_pte_t *ptep, >> struct stage2_map_data *data) >> @@ -495,6 +515,10 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level, >> put_page(page); >> } >> >> + /* Flush data cache before installation of the new PTE */ >> + if (stage2_pte_cacheable(new)) >> + stage2_flush_dcache(__va(phys), granule); >> + >> smp_store_release(ptep, new); >> get_page(page); >> data->phys += granule; >> @@ -651,20 +675,6 @@ int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size, >> return ret; >> } >> >> -static void stage2_flush_dcache(void *addr, u64 size) >> -{ >> - if (cpus_have_const_cap(ARM64_HAS_STAGE2_FWB)) >> - return; >> - >> - __flush_dcache_area(addr, size); >> -} >> - >> -static bool stage2_pte_cacheable(kvm_pte_t pte) >> -{ >> - u64 memattr = pte & KVM_PTE_LEAF_ATTR_LO_S2_MEMATTR; >> - return memattr == PAGE_S2_MEMATTR(NORMAL); >> -} >> - >> static int stage2_unmap_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep, >> enum kvm_pgtable_walk_flags flag, >> void * const arg) >> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c >> index 77cb2d28f2a4..d151927a7d62 100644 >> --- a/arch/arm64/kvm/mmu.c >> +++ b/arch/arm64/kvm/mmu.c >> @@ -609,11 +609,6 @@ void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm, >> kvm_mmu_write_protect_pt_masked(kvm, slot, gfn_offset, mask); >> } >> >> -static void clean_dcache_guest_page(kvm_pfn_t pfn, unsigned long size) >> -{ >> - __clean_dcache_guest_page(pfn, size); >> -} >> - >> static void invalidate_icache_guest_page(kvm_pfn_t pfn, unsigned long size) >> { >> __invalidate_icache_guest_page(pfn, size); >> @@ -882,9 +877,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >> if (writable) >> prot |= KVM_PGTABLE_PROT_W; >> >> - if (fault_status != FSC_PERM && !device) >> - clean_dcache_guest_page(pfn, vma_pagesize); >> - >> if (exec_fault) { >> prot |= KVM_PGTABLE_PROT_X; >> invalidate_icache_guest_page(pfn, vma_pagesize); > It seems that the I-side CMO now happens *before* the D-side, which > seems odd.
Yes, indeed. It is not so right in principle to put invalidation of icache before flush of dcache.
Thanks,
Yanan
> What prevents the CPU from speculatively fetching > instructions in the interval? I would also feel much more confident if > the two were kept close together. > > Thanks, > > M. >
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