From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-14.0 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8DA3BC4338F for ; Mon, 26 Jul 2021 10:35:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 77B3960F55 for ; Mon, 26 Jul 2021 10:35:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232450AbhGZJzD (ORCPT ); Mon, 26 Jul 2021 05:55:03 -0400 Received: from mail.kernel.org ([198.145.29.99]:37170 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231612AbhGZJyu (ORCPT ); Mon, 26 Jul 2021 05:54:50 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AED8860F22; Mon, 26 Jul 2021 10:35:12 +0000 (UTC) Received: from sofa.misterjones.org ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1m7xx0-0010R4-OE; Mon, 26 Jul 2021 11:35:10 +0100 Date: Mon, 26 Jul 2021 11:35:10 +0100 Message-ID: <87pmv5e529.wl-maz@kernel.org> From: Marc Zyngier To: Quentin Perret Cc: james.morse@arm.com, alexandru.elisei@arm.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, ardb@kernel.org, qwandor@google.com, tabba@google.com, dbrazdil@google.com, kernel-team@android.com Subject: Re: [PATCH v2 04/16] KVM: arm64: Optimize host memory aborts In-Reply-To: <20210726092905.2198501-5-qperret@google.com> References: <20210726092905.2198501-1-qperret@google.com> <20210726092905.2198501-5-qperret@google.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: qperret@google.com, james.morse@arm.com, alexandru.elisei@arm.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, ardb@kernel.org, qwandor@google.com, tabba@google.com, dbrazdil@google.com, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 26 Jul 2021 10:28:53 +0100, Quentin Perret wrote: > > The kvm_pgtable_stage2_find_range() function is used in the host memory > abort path to try and look for the largest block mapping that can be > used to map the faulting address. In order to do so, the function > currently walks the stage-2 page-table and looks for existing > incompatible mappings within the range of the largest possible block. > If incompatible mappings are found, it tries the same procedure again, > but using a smaller block range, and repeats until a matching range is > found (potentially up to page granularity). While this approach has > benefits (mostly in the fact that it proactively coalesces host stage-2 > mappings), it can be slow if the ranges are fragmented, and it isn't > optimized to deal with CPUs faulting on the same IPA as all of them will > do all the work every time. > > To avoid these issues, remove kvm_pgtable_stage2_find_range(), and walk > the page-table only once in the host_mem_abort() path to find the > closest leaf to the input address. With this, use the corresponding > range if it is invalid and not owned by another entity. If a valid leaf > is found, return -EAGAIN similar to what is done in the > kvm_pgtable_stage2_map() path to optimize concurrent faults. > > Signed-off-by: Quentin Perret > --- > arch/arm64/include/asm/kvm_pgtable.h | 30 ----------- > arch/arm64/kvm/hyp/nvhe/mem_protect.c | 39 +++++++++++++- > arch/arm64/kvm/hyp/pgtable.c | 74 --------------------------- > 3 files changed, 38 insertions(+), 105 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h > index 5a7a13bbd4a1..cec76a49f521 100644 > --- a/arch/arm64/include/asm/kvm_pgtable.h > +++ b/arch/arm64/include/asm/kvm_pgtable.h > @@ -141,16 +141,6 @@ enum kvm_pgtable_prot { > #define PAGE_HYP_RO (KVM_PGTABLE_PROT_R) > #define PAGE_HYP_DEVICE (PAGE_HYP | KVM_PGTABLE_PROT_DEVICE) > > -/** > - * struct kvm_mem_range - Range of Intermediate Physical Addresses > - * @start: Start of the range. > - * @end: End of the range. > - */ > -struct kvm_mem_range { > - u64 start; > - u64 end; > -}; > - > /** > * enum kvm_pgtable_walk_flags - Flags to control a depth-first page-table walk. > * @KVM_PGTABLE_WALK_LEAF: Visit leaf entries, including invalid > @@ -477,24 +467,4 @@ int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size, > */ > int kvm_pgtable_get_leaf(struct kvm_pgtable *pgt, u64 addr, > kvm_pte_t *ptep, u32 *level); > - > -/** > - * kvm_pgtable_stage2_find_range() - Find a range of Intermediate Physical > - * Addresses with compatible permission > - * attributes. > - * @pgt: Page-table structure initialised by kvm_pgtable_stage2_init*(). > - * @addr: Address that must be covered by the range. > - * @prot: Protection attributes that the range must be compatible with. > - * @range: Range structure used to limit the search space at call time and > - * that will hold the result. > - * > - * The offset of @addr within a page is ignored. An IPA is compatible with @prot > - * iff its corresponding stage-2 page-table entry has default ownership and, if > - * valid, is mapped with protection attributes identical to @prot. > - * > - * Return: 0 on success, negative error code on failure. > - */ > -int kvm_pgtable_stage2_find_range(struct kvm_pgtable *pgt, u64 addr, > - enum kvm_pgtable_prot prot, > - struct kvm_mem_range *range); > #endif /* __ARM64_KVM_PGTABLE_H__ */ > diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > index 871149246f5f..01700a908bb7 100644 > --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c > +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > @@ -159,6 +159,11 @@ static int host_stage2_unmap_dev_all(void) > return kvm_pgtable_stage2_unmap(pgt, addr, BIT(pgt->ia_bits) - addr); > } > > +struct kvm_mem_range { > + u64 start; > + u64 end; > +}; > + > static bool find_mem_range(phys_addr_t addr, struct kvm_mem_range *range) > { > int cur, left = 0, right = hyp_memblock_nr; > @@ -227,6 +232,38 @@ static inline int __host_stage2_idmap(u64 start, u64 end, > __ret; \ > }) > > +static int host_stage2_find_range(u64 addr, struct kvm_mem_range *range) nit: I find 'find_range' a bit odd. We already have found a range. We're just trying to narrow it down to something that fits in a single block mapping. How about 'host_stage2_adjust_range'? > +{ > + u64 granule, start, end; > + kvm_pte_t pte; > + u32 level; > + int ret; > + > + ret = kvm_pgtable_get_leaf(&host_kvm.pgt, addr, &pte, &level); > + if (ret) > + return ret; > + > + if (kvm_pte_valid(pte)) > + return -EAGAIN; > + > + if (pte) > + return -EPERM; > + > + do { > + granule = kvm_granule_size(level); > + start = ALIGN_DOWN(addr, granule); > + end = start + granule; > + level++; > + } while ((level < KVM_PGTABLE_MAX_LEVELS) && > + (!kvm_level_supports_block_mapping(level) || > + start < range->start || range->end < end)); > + This expression does my head in. You are trying to find the largest block mapping that entirely fits in range, right? Can we just express that directly (with a global negation for the purpose of the loop)? do { [...] } while (level < KVM_PGTABLE_MAX_LEVELS && !(kvm_level_supports_block_mapping(level) && start >= range->start && end <= range->end)); I personally find this much more readable, because it expresses the condition we are looking for rather than a lot of conditions forcing us to continue. You could also use a kvm_mem_range for the iteration, and add a helper that checks for the inclusion. > + range->start = start; > + range->end = end; > + > + return 0; > +} > + > static int host_stage2_idmap(u64 addr) > { > enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W; > @@ -238,7 +275,7 @@ static int host_stage2_idmap(u64 addr) > prot |= KVM_PGTABLE_PROT_X; > > hyp_spin_lock(&host_kvm.lock); > - ret = kvm_pgtable_stage2_find_range(&host_kvm.pgt, addr, prot, &range); > + ret = host_stage2_find_range(addr, &range); > if (ret) > goto unlock; Thanks, M. -- Without deviation from the norm, progress is not possible.