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From: Joao Martins <joao.m.martins@oracle.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
	"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
	"mgurtovoy@nvidia.com" <mgurtovoy@nvidia.com>,
	Linuxarm <linuxarm@huawei.com>,
	liulongfang <liulongfang@huawei.com>,
	"Zengtao (B)" <prime.zeng@hisilicon.com>,
	yuzenghui <yuzenghui@huawei.com>,
	Jonathan Cameron <jonathan.cameron@huawei.com>,
	"Wangzhou (B)" <wangzhou1@hisilicon.com>
Subject: Re: iommufd(+vfio-compat) dirty tracking
Date: Wed, 16 Mar 2022 20:37:58 +0000	[thread overview]
Message-ID: <c85a0d65-143e-6246-0d48-dec4e059e51a@oracle.com> (raw)
In-Reply-To: <6fd0bfdc-0918-e191-0170-abce6178ddaa@oracle.com>

On 3/16/22 16:36, Joao Martins wrote:
> On 3/15/22 19:29, Jason Gunthorpe wrote:
>> On Fri, Mar 11, 2022 at 01:51:32PM +0000, Joao Martins wrote:
>>> On 2/28/22 13:01, Joao Martins wrote:
>>>> On 2/25/22 20:44, Jason Gunthorpe wrote:
>>>>> On Fri, Feb 25, 2022 at 07:18:37PM +0000, Joao Martins wrote:
>>>>>> On 2/23/22 01:03, Jason Gunthorpe wrote:
>>>>>>> On Tue, Feb 22, 2022 at 11:55:55AM +0000, Joao Martins wrote:
>>>>> Questions I have:
>>>>>  - Do we need ranges for some reason? You mentioned ARM SMMU wants
>>>>>    ranges? how/what/why?
>>>>>

An amend here.

Sigh, ARM turns out is slightly more unique compared to x86. As I am re-reviewing
the ARM side. Apparently you have two controls: one is a 'feature bit'
just like x86 and another is a modifier (arm-only).

The Context descriptor (CD) equivalent to AMD DTEs or Intel context descriptor
equivalent for second-level. That's the top-level enabler to actually a *second*
modifier bit per-PTE (or per-TTD for more accurate terminology) which is the so
called DBM (dirty-bit-modifier). The latter when set, changes the meaning of
read/write access-flags of the PTE AP[2].

If you have CD.HD enabled (aka HTTU is enabled) *and* PTE.DBM set, then a
transition in the SMMU from "writable Clean" to "written" means that the the
access bits go from "read-only" (AP[2] = 1) to "read/write" (AP[2] = 0)
if-and-only-if PTE.DBM = 1 (and does not generate a permission IO page fault
like it normally would be with DBM = 0). Same thing for stage-2, except that
the access-bits are reversed (S2AP[1] is set when "written" and it's cleared
when it's "writable" (when DBM is also set).

Now you could say that this allows you to control on a per-range basis.
Gah, no, more like a per-PTE basis is more accurate.

And in practice I suppose that means that dynamically switching on/off SMMU
dirty-tracking *dynamically* means not only setting CD.HD but also walking the
page tables, and atomically setting/clearing both the DBM and AP[2].

References:

DDI0487H, Table D5-30 Data access permissions
SMMU 3.2 spec, 3.13.3 Dirty flag hardware update

  reply	other threads:[~2022-03-16 20:38 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-02  9:58 [RFC v2 0/4] vfio/hisilicon: add acc live migration driver Shameer Kolothum
2021-07-02  9:58 ` [RFC v2 1/4] hisi-acc-vfio-pci: add new vfio_pci driver for HiSilicon ACC devices Shameer Kolothum
2021-07-02 20:29   ` Alex Williamson
2021-07-05  7:20     ` Shameerali Kolothum Thodi
2021-07-04  7:03   ` Leon Romanovsky
2021-07-05  8:47     ` Shameerali Kolothum Thodi
2021-07-05  9:41       ` Max Gurtovoy
2021-07-05 10:18         ` Shameerali Kolothum Thodi
2021-07-05 18:27           ` Leon Romanovsky
2021-07-05 18:32             ` Jason Gunthorpe
2021-07-06  3:59               ` Leon Romanovsky
2021-07-06  4:39               ` Christoph Hellwig
2021-07-06 11:51                 ` Jason Gunthorpe
2021-07-02  9:58 ` [RFC v2 2/4] hisi_acc_vfio_pci: Override ioctl method to limit BAR2 region size Shameer Kolothum
2021-07-02 20:29   ` Alex Williamson
2021-07-05  7:22     ` Shameerali Kolothum Thodi
2021-07-02  9:58 ` [RFC v2 3/4] crypto: hisilicon/qm - Export mailbox functions for common use Shameer Kolothum
2021-07-04  9:34   ` Max Gurtovoy
2021-07-05 10:23     ` Shameerali Kolothum Thodi
2021-07-02  9:58 ` [RFC v2 4/4] hisi_acc_vfio_pci: Add support for vfio live migration Shameer Kolothum
2022-02-02 13:14 ` [RFC v2 0/4] vfio/hisilicon: add acc live migration driver Jason Gunthorpe
2022-02-02 14:34   ` Shameerali Kolothum Thodi
2022-02-02 15:39     ` Jason Gunthorpe
2022-02-02 16:10       ` Shameerali Kolothum Thodi
2022-02-02 17:03         ` Jason Gunthorpe
2022-02-02 19:05           ` Joao Martins
2022-02-03 15:18             ` Jason Gunthorpe
2022-02-04 19:53               ` Joao Martins
2022-02-04 23:07                 ` Jason Gunthorpe
2022-02-11 17:28                   ` Joao Martins
2022-02-11 17:49                     ` Jason Gunthorpe
2022-02-11 21:43                       ` Joao Martins
2022-02-12  0:01                         ` Jason Gunthorpe
2022-02-14 13:34                           ` Joao Martins
2022-02-14 14:06                             ` Jason Gunthorpe
2022-02-15 16:00                               ` Joao Martins
2022-02-15 16:21                                 ` Jason Gunthorpe
2022-02-22 11:55                                   ` Joao Martins
2022-02-23  1:03                                     ` Jason Gunthorpe
2022-02-25 19:18                                       ` Joao Martins
2022-02-25 20:44                                         ` Jason Gunthorpe
2022-02-28 13:01                                           ` Joao Martins
2022-02-28 21:01                                             ` Jason Gunthorpe
2022-03-01 13:06                                               ` Joao Martins
2022-03-01 13:54                                                 ` Jason Gunthorpe
2022-03-01 14:27                                                   ` Joao Martins
2022-03-11 13:51                                             ` iommufd(+vfio-compat) dirty tracking (Was: Re: [RFC v2 0/4] vfio/hisilicon: add acc live migration driver) Joao Martins
2022-03-15 19:29                                               ` Jason Gunthorpe
2022-03-16 16:36                                                 ` iommufd(+vfio-compat) dirty tracking Joao Martins
2022-03-16 20:37                                                   ` Joao Martins [this message]
2022-03-18 17:12                                                     ` Joao Martins
2022-03-18 17:34                                                       ` Jason Gunthorpe
2022-02-02 17:30     ` [RFC v2 0/4] vfio/hisilicon: add acc live migration driver Alex Williamson
2022-02-02 18:04       ` Jason Gunthorpe
2022-02-18 16:37 ` Jason Gunthorpe

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