From mboxrd@z Thu Jan 1 00:00:00 1970 From: Radim =?utf-8?B?S3LEjW3DocWZ?= Subject: Re: [PART2 PATCH v4 07/11] iommu/amd: Introduce amd_iommu_update_ga() Date: Wed, 13 Jul 2016 16:14:57 +0200 Message-ID: <20160713141457.GF21976@potion> References: <1468416032-7692-1-git-send-email-suravee.suthikulpanit@amd.com> <1468416032-7692-8-git-send-email-suravee.suthikulpanit@amd.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: joro@8bytes.org, pbonzini@redhat.com, alex.williamson@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, sherry.hurwitz@amd.com To: Suravee Suthikulpanit Return-path: Received: from mx1.redhat.com ([209.132.183.28]:33186 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751082AbcGMOPC (ORCPT ); Wed, 13 Jul 2016 10:15:02 -0400 Content-Disposition: inline In-Reply-To: <1468416032-7692-8-git-send-email-suravee.suthikulpanit@amd.com> Sender: kvm-owner@vger.kernel.org List-ID: [I pasted v3 reviews prefixed with a pipe where I think they still appl= y.] 2016-07-13 08:20-0500, Suravee Suthikulpanit: > From: Suravee Suthikulpanit >=20 > Introduces a new IOMMU API, amd_iommu_update_ga(), which allows > KVM (SVM) to update existing posted interrupt IOMMU IRTE when > load/unload vcpu. >=20 > Signed-off-by: Suravee Suthikulpanit > --- > diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c > @@ -4461,4 +4461,69 @@ int amd_iommu_create_irq_domain(struct amd_iom= mu *iommu) > +int amd_iommu_update_ga(u32 vcpu_id, u32 cpu, u32 vm_id, > + u64 base, bool is_run) |2016-07-13 15:49+0700, Suravee Suthikulpanit: |> On 07/12/2016 01:59 AM, Radim Kr=C4=8Dm=C3=A1=C5=99 wrote: |>> Not just in this function does the interface between svm and iommu = split |>> ga_tag into its two components (vcpu_id and ga_tag), but it seems t= hat |>> the combined value could always be used instead ... |>> Is there an advantage to passing two values? |> |> Here, the amd_iommu_update_ga() takes the two separate value for inp= ut |> parameters. Mainly the ga_tag (which is really the vm_id) and vcpu_i= d. This |> allow IOMMU driver to decide how to encode the GATAG to be programme= d into |> the IRTE. Currently, the actual GATAG is a 16-bit value, . |> This keeps the interface independent from how we encode the GATAG. I was thinking about making the IOMMU unaware how SVM or other Linux hypervisors use the ga_tag, i.e. passing the final u32 ga_tag. =46or example 32 bit hypervisor doesn't need to use lookup, because any pointer can used as the ga_tag directly. And there are other viable algoritms for assigning the ga_tag -- why isn't the vm_id 24 bits? > + unsigned long flags; > + struct amd_iommu *iommu; > + > + if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir)) > + return 0; > + > + for_each_iommu(iommu) { > + struct amd_ir_data *ir_data; > + > + spin_lock_irqsave(&iommu->gatag_ir_hash_lock, flags); > + > + /* Note: > + * We need to update all interrupt remapping table entries > + * for targeting the specified vcpu. Here, we use gatag > + * as a hash key and iterate through all entries in the bucket. > + */ > + hash_for_each_possible(iommu->gatag_ir_hash, ir_data, hnode, > + AMD_IOMMU_GATAG(vm_id, vcpu_id)) { > + struct irte_ga *irte =3D (struct irte_ga *) ir_data->entry; |>> (The ga_tag check is missing here too.) |> |> Here, the intention is to update all interrupt remapping entries in = the |> bucket w/ the same GATAG (i.e. vm_id + vcpu_id), where GATAG =3D |> AMD_IOMMU_GATAG(vm_id, vcpu_id). Which is why you need to check that AMD_IOMMU_GATAG(vm_id, vcpu_id) =3D=3D entry->fields_vapic.ga_tag The hashing function can map two different vm_id + vcpu_id to the same bucket and hash_for_each_possible() would return both of them, but only one belongs to the VCPU that we want to update. (And shouldn't there be only one match?) > + > + if (!irte->lo.fields_vapic.guest_mode) > + continue; > + > + update_irte_ga((struct irte_ga *)ir_data->ref, > + ir_data->irq_2_irte.devid, > + base, cpu, is_run); |>> (The lookup leading up to here is avoidable -- svm, the caller, has= the |>> ability to map ga_tag into irte/ir_data directly with a pointer. |>> I'm not sure if the lookup is slow enough to pardon optimization,= but |>> it might make the code simpler as well.) |>=20 |> I might have mislead you up to this point. Not sure if the assumptio= n here |> still hold with my explanation above. Sorry for confusion. SVM configures IOMMU with ga_tag, so IOMMU could return the pointer to ir_data/irte that was just configured. SVM would couple it with a VCPU (and hence a ga_tag) and when amd_iommu_update_ga() was needed, SVM would pass the ir_data/irte pointer directly, instead of looking it up though a ga_tag.