[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Xen-devel] Ping: [PATCH] x86: improve vCPU selection in pagetable_dying()
- To: Jan Beulich <JBeulich@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>
- From: George Dunlap <george.dunlap@xxxxxxxxxx>
- Date: Wed, 3 Oct 2018 17:56:06 +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: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 03 Oct 2018 16:56:19 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 09/26/2018 08:04 AM, Jan Beulich wrote:
>>>> On 25.09.18 at 18:22, <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 18/09/18 13:44, Jan Beulich wrote:
>>>>>> On 10.09.18 at 16:02, <JBeulich@xxxxxxxx> wrote:
>>>> Rather than unconditionally using vCPU 0, use the current vCPU if the
>>>> subject domain is the current one.
>>>>
>>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>
>> What improvement is this intended to bring?
>
> I've come across this quite a while ago when investigating possibly
> dangerous uses of d->vcpu[], well before your series to improve the
> situation there. I generally consider it wrong to hard code use of
> d->vcpu[0] whenever it can be avoided.
>
>> Shadows are per-domain, and the gmfn in question is passed in by the
>> caller. AFACIT, it is a logical bug that that the callback takes a vcpu
>> rather than a domain in the first place.
>
> Did you look at the 3-level variant of sh_pagetable_dying()? It very
> clearly reads the given vCPU's CR3.
Yes; and so the current implementation which unconditionally passes vcpu
0 is clearly a bug.
> Looking at things again (in particular
> the comment ahead of pagetable_dying()) I now actually wonder why
> HVMOP_pagetable_dying is permitted to be called by other than a domain
> for itself. There's no use of it in the tool stack. Disallowing the unused
> case would mean the fast-path logic in sh_pagetable_dying() could
> become the only valid/implemented case. Tim?
Not so -- a guest could still call pagetable_dying() on the top level PT
of a process not currently running.
I would be totally in favor of limiting this call to the guest itself,
however -- that would simplify the logic even more.
-George
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel
|
