From: Alexandru Stefan ISAILA <aisaila@bitdefender.com>
To: George Dunlap <george.dunlap@citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
Brian Woods <brian.woods@amd.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Tamas K Lengyel <tamas.lengyel@zentific.com>,
Paul Durrant <paul.durrant@citrix.com>, Tim Deegan <tim@xen.org>,
Razvan Cojocaru <rcojocaru@bitdefender.com>,
Jan Beulich <jbeulich@suse.com>
Subject: Re: [RFC PATCH 2/2] x86/mm: Add mem access rights to NPT
Date: Wed, 9 Jan 2019 09:30:59 +0000 [thread overview]
Message-ID: <821c3f9e-698d-7247-a095-6572e73d36d1@bitdefender.com> (raw)
In-Reply-To: <0f46782a-66f5-f2c6-4ed1-3e4dc4c7e6a7@citrix.com>
Ping
Suravee / Brian / Boris any ideas on this topic are appreciated.
Regards,
Alex
On 27.09.2018 13:37, George Dunlap wrote:
> On 09/26/2018 06:22 PM, Andrew Cooper wrote:
>> On 26/09/18 17:47, George Dunlap wrote:
>>> From: Isaila Alexandru <aisaila@bitdefender.com>
>>>
>>> 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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next prev parent reply other threads:[~2019-01-09 9:31 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-26 16:47 [RFC PATCH 1/2] mem_access: Fix npfec.kind propagation George Dunlap
2018-09-26 16:47 ` [RFC PATCH 2/2] x86/mm: Add mem access rights to NPT George Dunlap
2018-09-26 17:22 ` Andrew Cooper
2018-09-27 10:37 ` George Dunlap
2018-09-27 10:53 ` Paul Durrant
2019-01-09 9:30 ` Alexandru Stefan ISAILA [this message]
2018-09-27 9:38 ` Isaila Alexandru
2019-06-13 10:56 ` [Xen-devel] " Alexandru Stefan ISAILA
2019-06-17 10:48 ` George Dunlap
2019-06-17 11:58 ` Andrew Cooper
2019-06-13 15:19 ` Tamas Lengyel
2019-06-13 15:21 ` Razvan Cojocaru
2018-09-26 16:51 ` [RFC PATCH 1/2] mem_access: Fix npfec.kind propagation Tamas Lengyel
2018-09-26 17:00 ` Andrew Cooper
2018-09-27 7:04 ` Jan Beulich
2018-09-27 8:46 ` George Dunlap
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