From: Razvan Cojocaru <rcojocaru@bitdefender.com>
To: Jan Beulich <JBeulich@suse.com>, Tamas K Lengyel <tamas@tklengyel.com>
Cc: Wei Liu <wei.liu2@citrix.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
aisaila@bitdefender.com,
xen-devel <xen-devel@lists.xenproject.org>,
Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [PATCH v1] Fix p2m_set_suppress_ve
Date: Thu, 4 Apr 2019 15:46:00 +0300 [thread overview]
Message-ID: <0c0c0933-bf70-ac3d-57c8-68c14827bcae@bitdefender.com> (raw)
In-Reply-To: <5CA4D1880200007800224564@prv1-mh.provo.novell.com>
On 4/3/19 6:30 PM, Jan Beulich wrote:
>>>> On 03.04.19 at 17:17, <rcojocaru@bitdefender.com> wrote:
>> On 4/3/19 5:58 PM, Jan Beulich wrote:
>>>>>> On 03.04.19 at 16:29, <aisaila@bitdefender.com> wrote:
>>>> --- a/xen/arch/x86/mm/p2m.c
>>>> +++ b/xen/arch/x86/mm/p2m.c
>>>> @@ -3011,8 +3011,16 @@ int p2m_set_suppress_ve(struct domain *d, gfn_t gfn, bool suppress_ve,
>>>> mfn = p2m->get_entry(p2m, gfn, &t, &a, 0, NULL, NULL);
>>>> if ( !mfn_valid(mfn) )
>>>> {
>>>> - rc = -ESRCH;
>>>> - goto out;
>>>> + unsigned int page_order;
>>>> +
>>>> + mfn = __get_gfn_type_access(host_p2m, gfn_x(gfn), &t, &a,
>>>> + P2M_ALLOC | P2M_UNSHARE, &page_order, 0);
>>>
>>> I'm not entirely certain about P2M_ALLOC, but I'm pretty sure that
>>> at least P2M_UNSHARE is too heavy: Why would you want to force
>>> un-sharing of a page when all you want to alter is #VE behavior?
>>
>> That logic was taken from p2m_set_altp2m_mem_access(), we thought the
>> two cases are very similar.
>
> I see.
On the UNSHARE observation, we don't know why the author originally
requested the flag. We decided to keep it on the assumption that it
_probably_ handles some corner-case that somebody has come accross.
We'll prepare a mini-series factoring out the code we've been discussing
in separate functions: one for getting things out of the hostp2m if the
entry is not present in the altp2m, and one for the special
page-order-dependent code (which is duplicated in
p2m_set_altp2m_mem_access() and p2m_change_altp2m_gfn()).
Before going into that, are we now certain that ALLOC is sufficient? I
believe it should be for _our_ use-cases, but we don't want to break
anyone's code. Maybe Tamas knows more about this.
Thanks,
Razvan
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next prev parent reply other threads:[~2019-04-04 12:46 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-03 14:29 [PATCH v1] Fix p2m_set_suppress_ve Alexandru Stefan ISAILA
2019-04-03 14:58 ` Jan Beulich
2019-04-03 15:17 ` Razvan Cojocaru
2019-04-03 15:30 ` Jan Beulich
2019-04-03 15:48 ` Razvan Cojocaru
2019-04-03 16:04 ` Jan Beulich
2019-04-03 16:16 ` Tamas K Lengyel
2019-04-03 17:07 ` Razvan Cojocaru
2019-04-03 17:12 ` Tamas K Lengyel
2019-04-04 10:16 ` Jan Beulich
2019-04-03 17:41 ` Razvan Cojocaru
2019-04-04 10:47 ` Jan Beulich
2019-04-04 12:46 ` Razvan Cojocaru [this message]
2019-04-04 12:49 ` Andrew Cooper
2019-04-04 13:15 ` Tamas K Lengyel
2019-04-04 12:50 ` Razvan Cojocaru
2019-04-04 13:09 ` Tamas K Lengyel
2019-04-04 14:36 ` Jan Beulich
2019-04-04 14:43 ` Tamas K Lengyel
2019-04-04 14:51 ` Jan Beulich
2019-04-04 15:06 ` Tamas K Lengyel
2019-04-04 14:54 ` George Dunlap
2019-04-05 7:36 ` Jan Beulich
2019-04-05 7:36 ` [Xen-devel] " Jan Beulich
2019-04-05 13:59 ` Tamas K Lengyel
2019-04-05 13:59 ` [Xen-devel] " Tamas K Lengyel
2019-04-04 14:32 ` Jan Beulich
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