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[35.189.192.250]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49fe5dfa6a7sm129441475e9.12.2026.09.24.10.38.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Sep 2026 10:38:53 -0700 (PDT) Date: Thu, 24 Sep 2026 17:38:49 +0000 From: Mostafa Saleh To: Vincent Donnefort Cc: maz@kernel.org, oupton@kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, kernel-team@android.com, fuad.tabba@linux.dev, qperret@google.com, weilin.chang@arm.com, Keir Fraser Subject: Re: [PATCH v2 01/22] KVM: arm64: Prefault host stage-2 entries on block split Message-ID: References: <20260911135053.146435-1-vdonnefort@google.com> <20260911135053.146435-2-vdonnefort@google.com> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260911135053.146435-2-vdonnefort@google.com> On Fri, Sep 11, 2026 at 02:50:32PM +0100, 'Vincent Donnefort' via kernel-team wrote: > From: Keir Fraser > > For the host stage-2 that is idmap, we can avoid lazy-mapping on block > splitting by propagating existing valid mappings to neighbouring entries > of the new table. > > Signed-off-by: Keir Fraser > Co-developed-by: Quentin Perret > Signed-off-by: Quentin Perret > Signed-off-by: Vincent Donnefort > --- > arch/arm64/kvm/hyp/pgtable.c | 32 ++++++++++++++++++++++++++++++++ > 1 file changed, 32 insertions(+) > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > index b74dd5ce1efd..34f78a58cded 100644 > --- a/arch/arm64/kvm/hyp/pgtable.c > +++ b/arch/arm64/kvm/hyp/pgtable.c > @@ -1030,10 +1030,39 @@ static int stage2_map_walk_table_pre(const struct kvm_pgtable_visit_ctx *ctx, > return 0; > } > > +static void stage2_map_prefault_idmap(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t *ptep) > +{ > + kvm_pte_t block_pte = ctx->old; > + u64 pa; > + int i; > + > + if (!kvm_pte_valid(block_pte)) > + return; > + > + pa = ALIGN_DOWN(ctx->addr, kvm_granule_size(ctx->level)); > + for (i = 0; i < PTRS_PER_PTE; ++i, ++ptep, pa += kvm_granule_size(ctx->level + 1)) { > + kvm_pte_t pte = kvm_init_valid_leaf_pte(pa, block_pte, ctx->level + 1); > + > + /* > + * Skip ptes in the range being modified by the caller if we're > + * installing last level entries. Otherwise, we need to > + * temporarily put in a valid mapping to make sure the > + * prefaulting logic is triggered on the next > + * stage2_map_walk_leaf(). This adds an unnecessary TLBI as > + * we'll presumably re-break the freshly installed block, but > + * that should happen very infrequently. > + */ > + if ((ctx->level < (KVM_PGTABLE_LAST_LEVEL - 1)) || > + (pa < ctx->addr) || (pa >= ctx->end)) > + *ptep = pte; Do we need now to call get_page() on the table as we are installing a new PTE? Also, I think we need a WRITE_ONCE() for the PTE write. Thanks, Mostafa > + } > +} > + > static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx, > struct stage2_map_data *data) > { > struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops; > + struct kvm_pgtable *pgt = data->mmu->pgt; > kvm_pte_t *childp, new; > int ret; > > @@ -1051,6 +1080,9 @@ static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx, > if (!childp) > return -ENOMEM; > > + if (pgt->flags & KVM_PGTABLE_S2_IDMAP) > + stage2_map_prefault_idmap(ctx, childp); > + > if (!stage2_try_break_pte(ctx, data->mmu)) { > mm_ops->put_page(childp); > return -EAGAIN; > -- > 2.55.0.1007.g17ff1f9808-goog > > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. >