From: Juergen Gross <jgross@suse.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
Wei Liu <wei.liu2@citrix.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Ian Jackson <Ian.Jackson@eu.citrix.com>, Tim Deegan <tim@xen.org>,
Julien Grall <julien.grall@arm.com>,
xen-devel <xen-devel@lists.xenproject.org>,
Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [PATCH 1/3] xen: drop in_atomic()
Date: Fri, 24 May 2019 10:34:04 +0200 [thread overview]
Message-ID: <2a816b64-ae01-23e6-d287-1622e55bc295@suse.com> (raw)
In-Reply-To: <5CE791650200007800231DEA@prv1-mh.provo.novell.com>
On 24/05/2019 08:38, Jan Beulich wrote:
>>>> On 24.05.19 at 07:41, <jgross@suse.com> wrote:
>> On 22/05/2019 12:10, Jan Beulich wrote:
>>>>>> On 22.05.19 at 11:45, <jgross@suse.com> wrote:
>>>> --- a/xen/arch/x86/hvm/hvm.c
>>>> +++ b/xen/arch/x86/hvm/hvm.c
>>>> @@ -3185,22 +3185,6 @@ static enum hvm_translation_result __hvm_copy(
>>>>
>>>> ASSERT(is_hvm_vcpu(v));
>>>>
>>>> - /*
>>>> - * XXX Disable for 4.1.0: PV-on-HVM drivers will do grant-table ops
>>>> - * such as query_size. Grant-table code currently does copy_to/from_guest
>>>> - * accesses under the big per-domain lock, which this test would disallow.
>>>> - * The test is not needed until we implement sleeping-on-waitqueue when
>>>> - * we access a paged-out frame, and that's post 4.1.0 now.
>>>> - */
>>>> -#if 0
>>>> - /*
>>>> - * If the required guest memory is paged out, this function may sleep.
>>>> - * Hence we bail immediately if called from atomic context.
>>>> - */
>>>> - if ( in_atomic() )
>>>> - return HVMTRANS_unhandleable;
>>>> -#endif
>>>
>>> Dealing with this TODO item is of course much appreciated, but
>>> should it really be deleted altogether? The big-domain-lock issue
>>> is gone afair, in which case dropping the #if 0 would seem
>>> possible to me, even if it's not strictly needed without the sleep-
>>> on-waitqueue behavior mentioned.
>>
>> I just had a look and found the following path:
>>
>> do_domctl() (takes domctl_lock and hypercall_deadlock_mutex)
>> arch_do_domctl()
>> raw_copy_from_guest()
>> copy_from_user_hvm()
>> hvm_copy_from_guest_linear()
>> __hvm_copy()
>>
>> So no, we can't do the in_atomic() test IMO.
>
> Oh, right - that's a PVH constraint that could probably not even
> be thought of that the time the comment was written. I'm still
> of the opinion though that at least the still applicable part of
> the comment should be kept in place. Whether this means also
> keeping in_atomic() itself is then an independent question, i.e.
> I wouldn't consider it overly bad if there was no implementation
> in the tree, but the above still served as documentation of what
> would need to be re-added. Still my preference would be for it
> to be kept.
Would you be okay with replacing the removed stuff above with:
/*
* If the required guest memory is paged out this function may sleep.
* So in theory we should bail out if called in atomic context.
* Unfortunately this is true for PVH dom0 doing domctl calls which
* holds the domctl lock when accessing dom0 memory. OTOH dom0 memory
* should never be paged out, so we are fine without testing for
* atomic context.
*/
Juergen
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
WARNING: multiple messages have this Message-ID (diff)
From: Juergen Gross <jgross@suse.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
Wei Liu <wei.liu2@citrix.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Ian Jackson <Ian.Jackson@eu.citrix.com>, Tim Deegan <tim@xen.org>,
Julien Grall <julien.grall@arm.com>,
xen-devel <xen-devel@lists.xenproject.org>,
Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH 1/3] xen: drop in_atomic()
Date: Fri, 24 May 2019 10:34:04 +0200 [thread overview]
Message-ID: <2a816b64-ae01-23e6-d287-1622e55bc295@suse.com> (raw)
Message-ID: <20190524083404.srJ4cNUqyBlEEBRDoCvz-HW7qlq_L4zWYLPYrTvBiTk@z> (raw)
In-Reply-To: <5CE791650200007800231DEA@prv1-mh.provo.novell.com>
On 24/05/2019 08:38, Jan Beulich wrote:
>>>> On 24.05.19 at 07:41, <jgross@suse.com> wrote:
>> On 22/05/2019 12:10, Jan Beulich wrote:
>>>>>> On 22.05.19 at 11:45, <jgross@suse.com> wrote:
>>>> --- a/xen/arch/x86/hvm/hvm.c
>>>> +++ b/xen/arch/x86/hvm/hvm.c
>>>> @@ -3185,22 +3185,6 @@ static enum hvm_translation_result __hvm_copy(
>>>>
>>>> ASSERT(is_hvm_vcpu(v));
>>>>
>>>> - /*
>>>> - * XXX Disable for 4.1.0: PV-on-HVM drivers will do grant-table ops
>>>> - * such as query_size. Grant-table code currently does copy_to/from_guest
>>>> - * accesses under the big per-domain lock, which this test would disallow.
>>>> - * The test is not needed until we implement sleeping-on-waitqueue when
>>>> - * we access a paged-out frame, and that's post 4.1.0 now.
>>>> - */
>>>> -#if 0
>>>> - /*
>>>> - * If the required guest memory is paged out, this function may sleep.
>>>> - * Hence we bail immediately if called from atomic context.
>>>> - */
>>>> - if ( in_atomic() )
>>>> - return HVMTRANS_unhandleable;
>>>> -#endif
>>>
>>> Dealing with this TODO item is of course much appreciated, but
>>> should it really be deleted altogether? The big-domain-lock issue
>>> is gone afair, in which case dropping the #if 0 would seem
>>> possible to me, even if it's not strictly needed without the sleep-
>>> on-waitqueue behavior mentioned.
>>
>> I just had a look and found the following path:
>>
>> do_domctl() (takes domctl_lock and hypercall_deadlock_mutex)
>> arch_do_domctl()
>> raw_copy_from_guest()
>> copy_from_user_hvm()
>> hvm_copy_from_guest_linear()
>> __hvm_copy()
>>
>> So no, we can't do the in_atomic() test IMO.
>
> Oh, right - that's a PVH constraint that could probably not even
> be thought of that the time the comment was written. I'm still
> of the opinion though that at least the still applicable part of
> the comment should be kept in place. Whether this means also
> keeping in_atomic() itself is then an independent question, i.e.
> I wouldn't consider it overly bad if there was no implementation
> in the tree, but the above still served as documentation of what
> would need to be re-added. Still my preference would be for it
> to be kept.
Would you be okay with replacing the removed stuff above with:
/*
* If the required guest memory is paged out this function may sleep.
* So in theory we should bail out if called in atomic context.
* Unfortunately this is true for PVH dom0 doing domctl calls which
* holds the domctl lock when accessing dom0 memory. OTOH dom0 memory
* should never be paged out, so we are fine without testing for
* atomic context.
*/
Juergen
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
next prev parent reply other threads:[~2019-05-24 8:34 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-22 9:45 [PATCH 0/3] tune preempt_[dis|en]able() Juergen Gross
2019-05-22 9:45 ` [Xen-devel] " Juergen Gross
2019-05-22 9:45 ` [PATCH 1/3] xen: drop in_atomic() Juergen Gross
2019-05-22 9:45 ` [Xen-devel] " Juergen Gross
2019-05-22 9:58 ` Andrew Cooper
2019-05-22 9:58 ` [Xen-devel] " Andrew Cooper
2019-05-22 10:10 ` Jan Beulich
2019-05-22 10:10 ` [Xen-devel] " Jan Beulich
2019-05-24 5:41 ` Juergen Gross
2019-05-24 5:41 ` [Xen-devel] " Juergen Gross
2019-05-24 6:38 ` Jan Beulich
2019-05-24 6:38 ` [Xen-devel] " Jan Beulich
2019-05-24 8:34 ` Juergen Gross [this message]
2019-05-24 8:34 ` Juergen Gross
2019-05-24 8:39 ` Jan Beulich
2019-05-24 8:39 ` [Xen-devel] " Jan Beulich
2019-05-24 12:30 ` Andrew Cooper
2019-05-24 12:30 ` [Xen-devel] " Andrew Cooper
2019-05-24 12:35 ` Jan Beulich
2019-05-24 12:35 ` [Xen-devel] " Jan Beulich
[not found] ` <5CE52014020000780023147E@suse.com>
2019-05-22 10:19 ` Juergen Gross
2019-05-22 10:19 ` [Xen-devel] " Juergen Gross
2019-05-22 12:34 ` Jan Beulich
2019-05-22 12:34 ` [Xen-devel] " Jan Beulich
2019-05-22 9:45 ` [PATCH 2/3] xen: drop preempt_count() for non-debug builds Juergen Gross
2019-05-22 9:45 ` [Xen-devel] " Juergen Gross
2019-05-22 10:00 ` Andrew Cooper
2019-05-22 10:00 ` [Xen-devel] " Andrew Cooper
2019-05-22 10:17 ` Juergen Gross
2019-05-22 10:17 ` [Xen-devel] " Juergen Gross
2019-05-22 10:18 ` Jan Beulich
2019-05-22 10:18 ` [Xen-devel] " Jan Beulich
2019-05-22 10:39 ` Andrew Cooper
2019-05-22 10:39 ` [Xen-devel] " Andrew Cooper
2019-05-22 10:12 ` Jan Beulich
2019-05-22 10:12 ` [Xen-devel] " Jan Beulich
[not found] ` <5CE5207A0200007800231481@suse.com>
2019-05-22 10:17 ` Juergen Gross
2019-05-22 10:17 ` [Xen-devel] " Juergen Gross
2019-05-22 9:45 ` [PATCH 3/3] xen: build common/preempt.c only with CONFIG_DEBUG Juergen Gross
2019-05-22 9:45 ` [Xen-devel] " Juergen Gross
2019-05-22 13:01 [PATCH 1/3] xen: drop in_atomic() Juergen Gross
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=2a816b64-ae01-23e6-d287-1622e55bc295@suse.com \
--to=jgross@suse.com \
--cc=George.Dunlap@eu.citrix.com \
--cc=Ian.Jackson@eu.citrix.com \
--cc=JBeulich@suse.com \
--cc=andrew.cooper3@citrix.com \
--cc=julien.grall@arm.com \
--cc=konrad.wilk@oracle.com \
--cc=roger.pau@citrix.com \
--cc=sstabellini@kernel.org \
--cc=tim@xen.org \
--cc=wei.liu2@citrix.com \
--cc=xen-devel@lists.xenproject.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).