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Fri, 6 Nov 2026 09:02:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1793984554; bh=EC4LjuZjAr9z2qMOtu37LH8o0ZP8/mpIpNf7Oy6KkBg=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ovmLjpnsCd5acNSdYx8x+aPDwhAL9hTDpSSvryG7MvpsdYfIK8g03EmsPRwf4Y56P io4DrUZDl0HDVkK8/cZli/nHQmb8RPEtrKkvTt+7xySuNPKfSJE9PfYUMKFGDhA6AY RRqRBPZUTX7cS+oF+Bw8EilaMTITbPfM16Vncq34= Message-ID: <60fe23f4-4fca-41b6-8489-a28ab7b281f9@arm.com> Date: Fri, 6 Nov 2026 17:02:31 +0000 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RESEND v4 2/3] KVM: arm64: Introduce KVM_PGTABLE_WALK_SKIP_LEVEL* walk flags To: Leonardo Bras , Marc Zyngier , Oliver Upton , Fuad Tabba , Joey Gouly , Steffen Eiden , Zenghui Yu , Catalin Marinas , Will Deacon , Mark Rutland , Raghavendra Rao Ananta Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org References: <20261106161240.1345126-1-leo.bras@arm.com> <20261106161240.1345126-3-leo.bras@arm.com> Content-Language: en-US From: Suzuki K Poulose In-Reply-To: <20261106161240.1345126-3-leo.bras@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 06/11/2026 16:12, Leonardo Bras wrote: > Add new walking flags KVM_PGTABLE_WALK_SKIP_LEVEL{0-3}. > When used, they make the kvm_pgtable_walk() skip the given level, as well > as levels higher than that. > > Being able to skip levels substancially decreases the runtime of a minor nit: substantially > pagetable walk when the callback function does nothing on that level. > > Signed-off-by: Leonardo Bras > --- > arch/arm64/include/asm/kvm_pgtable.h | 14 ++++++++++++++ > arch/arm64/kvm/hyp/pgtable.c | 16 +++++++++++++--- > 2 files changed, 27 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h > index 41a8687938eb..5f37ceef8d63 100644 > --- a/arch/arm64/include/asm/kvm_pgtable.h > +++ b/arch/arm64/include/asm/kvm_pgtable.h > @@ -311,31 +311,45 @@ typedef bool (*kvm_pgtable_force_pte_cb_t)(u64 addr, u64 end, > * @KVM_PGTABLE_WALK_SHARED: Indicates the page-tables may be shared > * with other software walkers. > * @KVM_PGTABLE_WALK_IGNORE_EAGAIN: Don't terminate the walk early if > * the walker returns -EAGAIN. > * @KVM_PGTABLE_WALK_SKIP_BBM_TLBI: Visit and update table entries > * without Break-before-make's > * TLB invalidation. > * @KVM_PGTABLE_WALK_SKIP_CMO: Visit and update table entries > * without Cache maintenance > * operations required. > + * @KVM_PGTABLE_WALK_SKIP_LEVEL0: Skip visiting level 0+ entries > + * @KVM_PGTABLE_WALK_SKIP_LEVEL1: Skip visiting level 1+ entries > + * @KVM_PGTABLE_WALK_SKIP_LEVEL2: Skip visiting level 2+ entries > + * @KVM_PGTABLE_WALK_SKIP_LEVEL3: Skip visiting level 3 entries > */ > enum kvm_pgtable_walk_flags { > KVM_PGTABLE_WALK_LEAF = BIT(0), > KVM_PGTABLE_WALK_TABLE_PRE = BIT(1), > KVM_PGTABLE_WALK_TABLE_POST = BIT(2), > KVM_PGTABLE_WALK_SHARED = BIT(3), > KVM_PGTABLE_WALK_IGNORE_EAGAIN = BIT(4), > KVM_PGTABLE_WALK_SKIP_BBM_TLBI = BIT(5), > KVM_PGTABLE_WALK_SKIP_CMO = BIT(6), > + /* SKIP_LEVEL* flags should not be split nor reordered */ > + KVM_PGTABLE_WALK_SKIP_LEVEL0 = BIT(7), > + KVM_PGTABLE_WALK_SKIP_LEVEL1 = BIT(8), > + KVM_PGTABLE_WALK_SKIP_LEVEL2 = BIT(9), > + KVM_PGTABLE_WALK_SKIP_LEVEL3 = BIT(10), > }; > > +#define KVM_PGTABLE_WALK_SKIP_LEVELS (KVM_PGTABLE_WALK_SKIP_LEVEL0 | \ > + KVM_PGTABLE_WALK_SKIP_LEVEL1 | \ > + KVM_PGTABLE_WALK_SKIP_LEVEL2 | \ > + KVM_PGTABLE_WALK_SKIP_LEVEL3 ) > + > struct kvm_pgtable_visit_ctx { > kvm_pte_t *ptep; > kvm_pte_t old; > void *arg; > struct kvm_pgtable_mm_ops *mm_ops; > u64 start; > u64 addr; > u64 end; > s8 level; > enum kvm_pgtable_walk_flags flags; > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > index 7a51f78b6446..80744478c810 100644 > --- a/arch/arm64/kvm/hyp/pgtable.c > +++ b/arch/arm64/kvm/hyp/pgtable.c > @@ -137,20 +137,27 @@ static bool kvm_pgtable_walk_continue(const struct kvm_pgtable_walker *walker, > * Ignore the return code altogether for walkers outside a fault handler > * (e.g. write protecting a range of memory) and chug along with the > * page table walk. > */ > if (r == -EAGAIN) > return walker->flags & KVM_PGTABLE_WALK_IGNORE_EAGAIN; > > return !r; > } > > +static bool kvm_pgtable_skip_level(s8 level, enum kvm_pgtable_walk_flags flags) > +{ > + u32 skip = FIELD_GET(KVM_PGTABLE_WALK_SKIP_LEVELS, flags); > + > + return unlikely(skip && level >= ffs(skip) - 1); > +} > + > static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data, > struct kvm_pgtable_mm_ops *mm_ops, kvm_pteref_t pgtable, s8 level); > > static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data, > struct kvm_pgtable_mm_ops *mm_ops, > kvm_pteref_t pteref, s8 level) > { > enum kvm_pgtable_walk_flags flags = data->walker->flags; > kvm_pte_t *ptep = kvm_dereference_pteref(data->walker, pteref); > struct kvm_pgtable_visit_ctx ctx = { > @@ -185,35 +192,35 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data, > * into a newly installed or replaced table. > */ > if (reload) { > ctx.old = READ_ONCE(*ptep); > table = kvm_pte_table(ctx.old, level); > } > > if (!kvm_pgtable_walk_continue(data->walker, ret)) > return ret; > > - if (!table) { > + if (!table || kvm_pgtable_skip_level(level + 1, ctx.flags)) { > data->addr = ALIGN_DOWN(data->addr, kvm_granule_size(level)); > data->addr += kvm_granule_size(level); > goto out; > } > > childp = (kvm_pteref_t)kvm_pte_follow(ctx.old, mm_ops); > ret = __kvm_pgtable_walk(data, mm_ops, childp, level + 1); > if (!kvm_pgtable_walk_continue(data->walker, ret)) > return ret; > > - if (ctx.flags & KVM_PGTABLE_WALK_TABLE_POST) > +out: > + if (table && ctx.flags & KVM_PGTABLE_WALK_TABLE_POST) > ret = kvm_pgtable_visitor_cb(data, &ctx, KVM_PGTABLE_WALK_TABLE_POST); > > -out: > if (kvm_pgtable_walk_continue(data->walker, ret)) > return 0; > > return ret; > } > > static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data, > struct kvm_pgtable_mm_ops *mm_ops, kvm_pteref_t pgtable, s8 level) > { > u32 idx; > @@ -242,20 +249,23 @@ static int _kvm_pgtable_walk(struct kvm_pgtable *pgt, struct kvm_pgtable_walk_da > u32 idx; > int ret = 0; > u64 limit = BIT(pgt->ia_bits); > > if (data->addr > limit || data->end > limit) > return -ERANGE; > > if (!pgt->pgd) > return -EINVAL; > > + if (kvm_pgtable_skip_level(pgt->start_level, data->walker->flags)) > + return 0; > + Should we rather return an error here ? A walk skipping the start level, is that any meaningful ? Suzuki > for (idx = kvm_pgd_page_idx(pgt, data->addr); data->addr < data->end; ++idx) { > kvm_pteref_t pteref = &pgt->pgd[idx * PTRS_PER_PTE]; > > ret = __kvm_pgtable_walk(data, pgt->mm_ops, pteref, pgt->start_level); > if (ret) > break; > } > > return ret; > }