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[34.82.181.220]) by smtp.gmail.com with ESMTPSA id 8-20020a621408000000b0053e85a4a2ccsm8532407pfu.26.2022.09.13.17.53.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Sep 2022 17:53:21 -0700 (PDT) Date: Tue, 13 Sep 2022 17:53:17 -0700 From: Ricardo Koller To: Oliver Upton Cc: Marc Zyngier , James Morse , Alexandru Elisei , Suzuki K Poulose , Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, Quentin Perret , Reiji Watanabe , David Matlack , Ben Gardon , Paolo Bonzini , Gavin Shan , Peter Xu , Sean Christopherson , linux-kernel@vger.kernel.org Subject: Re: [PATCH 11/14] KVM: arm64: Make changes block->table to leaf PTEs parallel-aware Message-ID: References: <20220830194132.962932-1-oliver.upton@linux.dev> <20220830195102.964724-1-oliver.upton@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, Sep 13, 2022 at 05:51:55PM -0700, Ricardo Koller wrote: > On Tue, Aug 30, 2022 at 07:51:01PM +0000, Oliver Upton wrote: > > In order to service stage-2 faults in parallel, stage-2 table walkers > > must take exclusive ownership of the PTE being worked on. An additional > > requirement of the architecture is that software must perform a > > 'break-before-make' operation when changing the block size used for > > mapping memory. > > > > Roll these two concepts together into helpers for performing a > > 'break-before-make' sequence. Use a special PTE value to indicate a PTE > > has been locked by a software walker. Additionally, use an atomic > > compare-exchange to 'break' the PTE when the stage-2 page tables are > > possibly shared with another software walker. Elide the DSB + TLBI if > > the evicted PTE was invalid (and thus not subject to break-before-make). > > > > All of the atomics do nothing for now, as the stage-2 walker isn't fully > > ready to perform parallel walks. > > > > Signed-off-by: Oliver Upton > > --- > > arch/arm64/kvm/hyp/pgtable.c | 87 +++++++++++++++++++++++++++++++++--- > > 1 file changed, 82 insertions(+), 5 deletions(-) > > > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > > index 61a4437c8c16..71ae96608752 100644 > > --- a/arch/arm64/kvm/hyp/pgtable.c > > +++ b/arch/arm64/kvm/hyp/pgtable.c > > @@ -49,6 +49,12 @@ > > #define KVM_INVALID_PTE_OWNER_MASK GENMASK(9, 2) > > #define KVM_MAX_OWNER_ID 1 > > > > +/* > > + * Used to indicate a pte for which a 'break-before-make' sequence is in > > + * progress. > > + */ > > +#define KVM_INVALID_PTE_LOCKED BIT(10) > > + > > struct kvm_pgtable_walk_data { > > struct kvm_pgtable *pgt; > > struct kvm_pgtable_walker *walker; > > @@ -586,6 +592,8 @@ struct stage2_map_data { > > > > /* Force mappings to page granularity */ > > bool force_pte; > > + > > + bool shared; > > }; > > > > u64 kvm_get_vtcr(u64 mmfr0, u64 mmfr1, u32 phys_shift) > > @@ -691,6 +699,11 @@ static bool stage2_pte_is_counted(kvm_pte_t pte) > > return kvm_pte_valid(pte) || kvm_invalid_pte_owner(pte); > > } > > > > +static bool stage2_pte_is_locked(kvm_pte_t pte) > > +{ > > + return !kvm_pte_valid(pte) && (pte & KVM_INVALID_PTE_LOCKED); > > +} > > + > > static bool stage2_try_set_pte(kvm_pte_t *ptep, kvm_pte_t old, kvm_pte_t new, bool shared) > > { > > if (!shared) { > > @@ -701,6 +714,69 @@ static bool stage2_try_set_pte(kvm_pte_t *ptep, kvm_pte_t old, kvm_pte_t new, bo > > return cmpxchg(ptep, old, new) == old; > > } > > > > +/** > > + * stage2_try_break_pte() - Invalidates a pte according to the > > + * 'break-before-make' requirements of the > > + * architecture. > > + * > > + * @ptep: Pointer to the pte to break > > + * @old: The previously observed value of the pte > > + * @addr: IPA corresponding to the pte > > + * @level: Table level of the pte > > + * @shared: true if the stage-2 page tables could be shared by multiple software > > + * walkers > > + * > > + * Returns: true if the pte was successfully broken. > > + * > > + * If the removed pte was valid, performs the necessary serialization and TLB > > + * invalidation for the old value. For counted ptes, drops the reference count > > + * on the containing table page. > > + */ > > +static bool stage2_try_break_pte(kvm_pte_t *ptep, kvm_pte_t old, u64 addr, u32 level, > > + struct stage2_map_data *data) > > +{ > > + struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops; > > + > > + if (stage2_pte_is_locked(old)) { > > + /* > > + * Should never occur if this walker has exclusive access to the > > + * page tables. > > + */ > > + WARN_ON(!data->shared); > > + return false; > > + } > > The above check is not needed as the cmpxchg() will return false if the > old pte is equal to "new" (KVM_INVALID_PTE_LOCKED). > > > + > > + if (!stage2_try_set_pte(ptep, old, KVM_INVALID_PTE_LOCKED, data->shared)) > > + return false; > > + > > + /* > > + * Perform the appropriate TLB invalidation based on the evicted pte > > + * value (if any). > > + */ > > + if (kvm_pte_table(old, level)) > > + kvm_call_hyp(__kvm_tlb_flush_vmid, data->mmu); > > + else if (kvm_pte_valid(old)) > > + kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, data->mmu, addr, level); > > + > > + if (stage2_pte_is_counted(old)) > > + mm_ops->put_page(ptep); > > + > > + return true; > > +} > > + > > +static void stage2_make_pte(kvm_pte_t *ptep, kvm_pte_t old, kvm_pte_t new, > > + struct stage2_map_data *data) > > +{ nit: old is not used > > + struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops; > > + > > + WARN_ON(!stage2_pte_is_locked(*ptep)); > > + > > + if (stage2_pte_is_counted(new)) > > + mm_ops->get_page(ptep); > > + > > + smp_store_release(ptep, new); > > +} > > + > > 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) > > { > > @@ -836,17 +912,18 @@ static int stage2_map_walk_leaf(u64 addr, u64 end, u32 level, kvm_pte_t *ptep, > > if (!childp) > > return -ENOMEM; > > > > + if (!stage2_try_break_pte(ptep, *old, addr, level, data)) { > > + mm_ops->put_page(childp); > > + return -EAGAIN; > > + } > > + > > /* > > * If we've run into an existing block mapping then replace it with > > * a table. Accesses beyond 'end' that fall within the new table > > * will be mapped lazily. > > */ > > - if (stage2_pte_is_counted(pte)) > > - stage2_put_pte(ptep, data->mmu, addr, level, mm_ops); > > - > > new = kvm_init_table_pte(childp, mm_ops); > > - mm_ops->get_page(ptep); > > - smp_store_release(ptep, new); > > + stage2_make_pte(ptep, *old, new, data); > > *old = new; > > > > return 0; > > -- > > 2.37.2.672.g94769d06f0-goog > >