Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753411AbbEAGxR (ORCPT ); Fri, 1 May 2015 02:53:17 -0400 Received: from mail-pa0-f52.google.com ([209.85.220.52]:33796 "EHLO mail-pa0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751828AbbEAGxP (ORCPT ); Fri, 1 May 2015 02:53:15 -0400 Message-ID: <554322D4.7070508@ozlabs.ru> Date: Fri, 01 May 2015 16:53:08 +1000 From: Alexey Kardashevskiy User-Agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: David Gibson CC: linuxppc-dev@lists.ozlabs.org, Benjamin Herrenschmidt , Paul Mackerras , Alex Williamson , Gavin Shan , linux-kernel@vger.kernel.org Subject: Re: [PATCH kernel v9 27/32] powerpc/iommu/ioda2: Add get_table_size() to calculate the size of future table References: <1429964096-11524-1-git-send-email-aik@ozlabs.ru> <1429964096-11524-28-git-send-email-aik@ozlabs.ru> <20150429064029.GX32589@voom.redhat.com> <5542FCD2.9000601@ozlabs.ru> <20150501051247.GP24886@voom.redhat.com> In-Reply-To: <20150501051247.GP24886@voom.redhat.com> Content-Type: text/plain; charset=koi8-r; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6827 Lines: 161 On 05/01/2015 03:12 PM, David Gibson wrote: > On Fri, May 01, 2015 at 02:10:58PM +1000, Alexey Kardashevskiy wrote: >> On 04/29/2015 04:40 PM, David Gibson wrote: >>> On Sat, Apr 25, 2015 at 10:14:51PM +1000, Alexey Kardashevskiy wrote: >>>> This adds a way for the IOMMU user to know how much a new table will >>>> use so it can be accounted in the locked_vm limit before allocation >>>> happens. >>>> >>>> This stores the allocated table size in pnv_pci_create_table() >>>> so the locked_vm counter can be updated correctly when a table is >>>> being disposed. >>>> >>>> This defines an iommu_table_group_ops callback to let VFIO know >>>> how much memory will be locked if a table is created. >>>> >>>> Signed-off-by: Alexey Kardashevskiy >>>> --- >>>> Changes: >>>> v9: >>>> * reimplemented the whole patch >>>> --- >>>> arch/powerpc/include/asm/iommu.h | 5 +++++ >>>> arch/powerpc/platforms/powernv/pci-ioda.c | 14 ++++++++++++ >>>> arch/powerpc/platforms/powernv/pci.c | 36 +++++++++++++++++++++++++++++++ >>>> arch/powerpc/platforms/powernv/pci.h | 2 ++ >>>> 4 files changed, 57 insertions(+) >>>> >>>> diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h >>>> index 1472de3..9844c106 100644 >>>> --- a/arch/powerpc/include/asm/iommu.h >>>> +++ b/arch/powerpc/include/asm/iommu.h >>>> @@ -99,6 +99,7 @@ struct iommu_table { >>>> unsigned long it_size; /* Size of iommu table in entries */ >>>> unsigned long it_indirect_levels; >>>> unsigned long it_level_size; >>>> + unsigned long it_allocated_size; >>>> unsigned long it_offset; /* Offset into global table */ >>>> unsigned long it_base; /* mapped address of tce table */ >>>> unsigned long it_index; /* which iommu table this is */ >>>> @@ -155,6 +156,10 @@ extern struct iommu_table *iommu_init_table(struct iommu_table * tbl, >>>> struct iommu_table_group; >>>> >>>> struct iommu_table_group_ops { >>>> + unsigned long (*get_table_size)( >>>> + __u32 page_shift, >>>> + __u64 window_size, >>>> + __u32 levels); >>>> long (*create_table)(struct iommu_table_group *table_group, >>>> int num, >>>> __u32 page_shift, >>>> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c >>>> index e0be556..7f548b4 100644 >>>> --- a/arch/powerpc/platforms/powernv/pci-ioda.c >>>> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c >>>> @@ -2062,6 +2062,18 @@ static void pnv_pci_ioda2_setup_bypass_pe(struct pnv_phb *phb, >>>> } >>>> >>>> #ifdef CONFIG_IOMMU_API >>>> +static unsigned long pnv_pci_ioda2_get_table_size(__u32 page_shift, >>>> + __u64 window_size, __u32 levels) >>>> +{ >>>> + unsigned long ret = pnv_get_table_size(page_shift, window_size, levels); >>>> + >>>> + if (!ret) >>>> + return ret; >>>> + >>>> + /* Add size of it_userspace */ >>>> + return ret + (window_size >> page_shift) * sizeof(unsigned long); >>> >>> This doesn't make much sense. The userspace view can't possibly be a >>> property of the specific low-level IOMMU model. >> >> >> This it_userspace thing is all about memory preregistration. >> >> I need some way to track how many actual mappings the >> mm_iommu_table_group_mem_t has in order to decide whether to allow >> unregistering or not. >> >> When I clear TCE, I can read the old value which is host physical address >> which I cannot use to find the preregistered region and adjust the mappings >> counter; I can only use userspace addresses for this (not even guest >> physical addresses as it is VFIO and probably no KVM). >> >> So I have to keep userspace addresses somewhere, one per IOMMU page, and the >> iommu_table seems a natural place for this. > > Well.. sort of. But as noted elsewhere this pulls VFIO specific > constraints into a platform code structure. And whether you get this > table depends on the platform IOMMU type rather than on what VFIO > wants to do with it, which doesn't make sense. > > What might make more sense is an opaque pointer io iommu_table for use > by the table "owner" (in the take_ownership sense). The pointer would > be stored in iommu_table, but VFIO is responsible for populating and > managing its contents. > > Or you could just put the userspace mappings in the container. > Although you might want a different data structure in that case. Nope. I need this table in in-kernel acceleration to update the mappings counter per mm_iommu_table_group_mem_t. In KVM's real mode handlers, I only have IOMMU tables, not containers or groups. QEMU creates a guest view of the table (KVM_CREATE_SPAPR_TCE) specifying a LIOBN, and then attaches TCE tables to it via set of ioctls (one per IOMMU group) to VFIO KVM device. So if I call it it_opaque (instead of it_userspace), I will still need a common place (visible to VFIO and PowerKVM) for this to put: #define IOMMU_TABLE_USERSPACE_ENTRY(tbl, entry) So far this place was arch/powerpc/include/asm/iommu.h and the iommu_table struct. > The other thing to bear in mind is that registered regions are likely > to be large contiguous blocks in user addresses, though obviously not > contiguous in physical addr. So you might be able to compaticfy this > information by storing it as a list of variable length blocks in > userspace address space, rather than a per-page address.. It is 8 bytes per system page - 8/65536 = 0.00012 (or 26MB for 200GB guest) - very little overhead. > But.. isn't there a bigger problem here. As Paulus was pointing out, > there's nothing guaranteeing the page tables continue to contain the > same page as was there at gup() time. This can happen if the userspace remaps memory which it registered/mapped for DMA via VFIO, no? If so, then the userspace just should not do this, it is DMA, it cannot be moved like this. What am I missing here? > What's going to happen if you REGISTER a memory region, then mremap() > over it? The registered pages will remain pinned and PUT_TCE will use that region for translation (and this will fail as the userspace addresses changed). I do not see how it is different from the situation when the userspace mapped a page and mremap()ed it while it is DMA-mapped. > Then attempt to PUT_TCE a page in the region? Or what if you > mremap() it to someplace else then try to PUT_TCE a page there? This will fail - a new userspace address has to be preregistered. > Or REGISTER it again in its new location? It will be pinned twice + some memory overhead to store the same host physical address(es) twice. -- Alexey -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/