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Re: [Xen-devel] [RFC PATCH 2/2] x86/mm: Add mem access rights to NPT
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: George Dunlap <george.dunlap@xxxxxxxxxx>
- Date: Thu, 27 Sep 2018 11:37:48 +0100
- Autocrypt: addr=george.dunlap@xxxxxxxxxx; prefer-encrypt=mutual; keydata= xsFNBFPqG+MBEACwPYTQpHepyshcufo0dVmqxDo917iWPslB8lauFxVf4WZtGvQSsKStHJSj 92Qkxp4CH2DwudI8qpVbnWCXsZxodDWac9c3PordLwz5/XL41LevEoM3NWRm5TNgJ3ckPA+J K5OfSK04QtmwSHFP3G/SXDJpGs+oDJgASta2AOl9vPV+t3xG6xyfa2NMGn9wmEvvVMD44Z7R W3RhZPn/NEZ5gaJhIUMgTChGwwWDOX0YPY19vcy5fT4bTIxvoZsLOkLSGoZb/jHIzkAAznug Q7PPeZJ1kXpbW9EHHaUHiCD9C87dMyty0N3TmWfp0VvBCaw32yFtM9jUgB7UVneoZUMUKeHA fgIXhJ7I7JFmw3J0PjGLxCLHf2Q5JOD8jeEXpdxugqF7B/fWYYmyIgwKutiGZeoPhl9c/7RE Bf6f9Qv4AtQoJwtLw6+5pDXsTD5q/GwhPjt7ohF7aQZTMMHhZuS52/izKhDzIufl6uiqUBge 0lqG+/ViLKwCkxHDREuSUTtfjRc9/AoAt2V2HOfgKORSCjFC1eI0+8UMxlfdq2z1AAchinU0 eSkRpX2An3CPEjgGFmu2Je4a/R/Kd6nGU8AFaE8ta0oq5BSFDRYdcKchw4TSxetkG6iUtqOO ZFS7VAdF00eqFJNQpi6IUQryhnrOByw+zSobqlOPUO7XC5fjnwARAQABzSRHZW9yZ2UgVy4g RHVubGFwIDxkdW5sYXBnQHVtaWNoLmVkdT7CwYAEEwEKACoCGwMFCwkIBwMFFQoJCAsFFgID AQACHgECF4ACGQEFAlpk2IEFCQo9I54ACgkQpjY8MQWQtG1A1BAAnc0oX3+M/jyv4j/ESJTO U2JhuWUWV6NFuzU10pUmMqpgQtiVEVU2QbCvTcZS1U/S6bqAUoiWQreDMSSgGH3a3BmRNi8n HKtarJqyK81aERM2HrjYkC1ZlRYG+jS8oWzzQrCQiTwn3eFLJrHjqowTbwahoiMw/nJ+OrZO /VXLfNeaxA5GF6emwgbpshwaUtESQ/MC5hFAFmUBZKAxp9CXG2ZhTP6ROV4fwhpnHaz8z+BT NQz8YwA4gkmFJbDUA9I0Cm9D/EZscrCGMeaVvcyldbMhWS+aH8nbqv6brhgbJEQS22eKCZDD J/ng5ea25QnS0fqu3bMrH39tDqeh7rVnt8Yu/YgOwc3XmgzmAhIDyzSinYEWJ1FkOVpIbGl9 uR6seRsfJmUK84KCScjkBhMKTOixWgNEQ/zTcLUsfTh6KQdLTn083Q5aFxWOIal2hiy9UyqR VQydowXy4Xx58rqvZjuYzdGDdAUlZ+D2O3Jp28ez5SikA/ZaaoGI9S1VWvQsQdzNfD2D+xfL qfd9yv7gko9eTJzv5zFr2MedtRb/nCrMTnvLkwNX4abB5+19JGneeRU4jy7yDYAhUXcI/waS /hHioT9MOjMh+DoLCgeZJYaOcgQdORY/IclLiLq4yFnG+4Ocft8igp79dbYYHkAkmC9te/2x Kq9nEd0Hg288EO/OwE0EVFq6vQEIAO2idItaUEplEemV2Q9mBA8YmtgckdLmaE0uzdDWL9To 1PL+qdNe7tBXKOfkKI7v32fe0nB4aecRlQJOZMWQRQ0+KLyXdJyHkq9221sHzcxsdcGs7X3c 17ep9zASq+wIYqAdZvr7pN9a3nVHZ4W7bzezuNDAvn4EpOf/o0RsWNyDlT6KECs1DuzOdRqD oOMJfYmtx9hMzqBoTdr6U20/KgnC/dmWWcJAUZXaAFp+3NYRCkk7k939VaUpoY519CeLrymd Vdke66KCiWBQXMkgtMGvGk5gLQLy4H3KXvpXoDrYKgysy7jeOccxI8owoiOdtbfM8TTDyWPR Ygjzb9LApA8AEQEAAcLBZQQYAQoADwIbDAUCWmTXMwUJB+tP9gAKCRCmNjwxBZC0bb+2D/9h jn1k5WcRHlu19WGuH6q0Kgm1LRT7PnnSz904igHNElMB5a7wRjw5kdNwU3sRm2nnmHeOJH8k Yj2Hn1QgX5SqQsysWTHWOEseGeoXydx9zZZkt3oQJM+9NV1VjK0bOXwqhiQyEUWz5/9l467F S/k4FJ5CHNRumvhLa0l2HEEu5pxq463HQZHDt4YE/9Y74eXOnYCB4nrYxQD/GSXEZvWryEWr eDoaFqzq1TKtzHhFgQG7yFUEepxLRUUtYsEpT6Rks2l4LCqG3hVD0URFIiTyuxJx3VC2Ta4L H3hxQtiaIpuXqq2D4z63h6vCx2wxfZc/WRHGbr4NAlB81l35Q/UHyMocVuYLj0llF0rwU4Aj iKZ5qWNSEdvEpL43fTvZYxQhDCjQTKbb38omu5P4kOf1HT7s+kmQKRtiLBlqHzK17D4K/180 ADw7a3gnmr5RumcZP3NGSSZA6jP5vNqQpNu4gqrPFWNQKQcW8HBiYFgq6SoLQQWbRxJDHvTR YJ2ms7oCe870gh4D1wFFqTLeyXiVqjddENGNaP8ZlCDw6EU82N8Bn5LXKjR1GWo2UK3CjrkH pTt3YYZvrhS2MO2EYEcWjyu6LALF/lS6z6LKeQZ+t9AdQUcILlrx9IxqXv6GvAoBLJY1jjGB q+/kRPrWXpoaQn7FXWGfMqU+NkY9enyrlw==
- Cc: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>, Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>, Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Paul Durrant <paul.durrant@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Isaila Alexandru <aisaila@xxxxxxxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Brian Woods <brian.woods@xxxxxxx>
- Delivery-date: Thu, 27 Sep 2018 10:38:05 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 09/26/2018 06:22 PM, Andrew Cooper wrote:
> On 26/09/18 17:47, George Dunlap wrote:
>> From: Isaila Alexandru <aisaila@xxxxxxxxxxxxxxx>
>>
>> This patch adds access control for NPT mode.
>>
>> There aren’t enough extra bits to store the access rights in the NPT p2m
>> table, so we add a radix tree to store extra information.
>
> I'm sorry to re-open this argument, but why?
>
> ISTR there being some argument based on pagetable sharing with the
> IOMMU, but that doesn't work at the moment and can't reasonably be made
> to work. For one, attempting to use pt sharing will break as soon as
> you try and DMA to a mapped grant.
>
> I'm disinclined to let a broken vestigial feature get in the way of real
> improvements.
>
> Beyond that, an NPT PTE has basically the same number of software
> available bits as an EPT PTE.
>
> Am I missing anything?
Wow -- looks like IOMMU/p2m sharing has been disabled unconditionally
since 2014. If nobody has complained since then, that seems like a good
enough reason to me to rip it out.
Suravee / Brian / Boris -- any opinions?
The main reason to go with the 'extra bits' solution rather than the
'rip out iommu/p2m sharing' solution is because people have been
prognosticating for years that we would be running out of bits and need
more at some point in the future. I thought Paul, for instance, might
have a use for the extra bits. But I'm happy to wait until such time as
we need it and then fish this patch out of the mail archives.
-George
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