From: "Jan Beulich" <JBeulich@suse.com>
To: Razvan Cojocaru <rcojocaru@bitdefender.com>,
Tamas K Lengyel <tamas@tklengyel.com>
Cc: Xen-devel <xen-devel@lists.xenproject.org>,
Julien Grall <julien.grall@arm.com>,
Stefano Stabellini <sstabellini@kernel.org>
Subject: Re: [PATCH v4 5/8] arm/vm_event: get/set registers
Date: Thu, 02 Jun 2016 03:38:21 -0600 [thread overview]
Message-ID: <57501AAE02000078000F0CDE@prv-mh.provo.novell.com> (raw)
In-Reply-To: <8da9b1a2-450a-62e5-2f0c-89f58a7857be@bitdefender.com>
>>> On 02.06.16 at 10:26, <rcojocaru@bitdefender.com> wrote:
> On 06/02/2016 10:35 AM, Jan Beulich wrote:
>> The criteria for inclusion or exclusion should
>> follow a predictable model. I.e. if someone comes along and says
>> "I need register Y", then there should be rules that (s)he can apply
>> up front to determine what (at least in the vast majority of cases)
>> the response is going to be. You saying "I need only this arbitrary
>> subset of registers" is completely in-transparent, as it leaves open
>> why this is so, and why this would also be so for others. I.e. you'd
>> at least need to answer the question why (as an example) you
>> need x5 included, but not x25, despite both registers being equal
>> from an architecture pov. An answer like "My application gets away
>> with it" is not acceptable here.
>
> There will be trade-offs. Again, my preference would be to have a
> multi-page ring buffer with all the VCPU context included in the
> request, always. This would work best as far as both completeness and
> performance goes.
>
> But that is obviously not a trivial change and I can see how Tamas would
> prefer to get things done sooner along the lines of the pre-existing
> design (whatever its merits and demerits are).
>
> As long as we're using a smaller ring buffer, the answer (at least as
> I've meant it) is not "_my_ application gets away with it" - which is
> indeed not the most reasonable statement, but "_current_ introspection
> applications - of which my application is one of - don't need more than
> this at this time".
But then could one of you finally say _why_ that is? I.e. why some
GPRs are "better" to your applications than others? If you need
access to _any_ GPRs that don't have a special purpose (like PC,
SP, LR, and maybe FP; I realize this is more applicable to ARM32
than ARM64), I would suspect you need them to e.g. obtain
instruction operands. Yet then I can't see why some of them are
needed while others aren't. I could mayve see you wanting access
to function argument and return value registers, but afaict the
proposed set isn't matching that set either, plus that's a guest ABI
thing anyway, i.e. would again be arbitrary due to you limiting
things to work with just certain guests.
Jan
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next prev parent reply other threads:[~2016-06-02 9:38 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-29 22:37 [PATCH v4 1/8] monitor: Rename vm_event_monitor_get_capabilities Tamas K Lengyel
2016-05-29 22:37 ` [PATCH v4 2/8] monitor: Rename vm_event_monitor_guest_request Tamas K Lengyel
2016-05-30 7:05 ` Razvan Cojocaru
2016-05-30 13:51 ` Jan Beulich
2016-05-29 22:37 ` [PATCH v4 3/8] monitor: Rename hvm/event to hvm/monitor Tamas K Lengyel
2016-05-30 7:08 ` Razvan Cojocaru
2016-05-30 13:53 ` Jan Beulich
2016-05-29 22:37 ` [PATCH v4 4/8] monitor: ARM SMC events Tamas K Lengyel
2016-06-01 11:37 ` Julien Grall
[not found] ` <CABfawhmO9tUG3-OcorfwqdOgZTkjoUk+u=dHySGonBDvobqyKw@mail.gmail.com>
[not found] ` <CABfawhmK2GAmQqZMhrgjYzeUZ_XaoyRUPuJxyPK5LJEHwsp5SA@mail.gmail.com>
[not found] ` <CABfawh=J1fwinTYKGvJNrFPOsGLSXz6U3GE8fxPz3-KsXSWfbQ@mail.gmail.com>
[not found] ` <CABfawhn7zvE=hn0hq1ryH+sW-jdkAXgZM1C2KxwZVUE8pbp8cQ@mail.gmail.com>
2016-06-01 15:41 ` Tamas K Lengyel
2016-06-02 14:23 ` Julien Grall
2016-06-02 22:31 ` Tamas K Lengyel
2016-07-04 19:13 ` Tamas K Lengyel
2016-07-04 20:02 ` Julien Grall
2016-07-04 21:05 ` Tamas K Lengyel
2016-07-05 9:58 ` Julien Grall
2016-05-29 22:37 ` [PATCH v4 5/8] arm/vm_event: get/set registers Tamas K Lengyel
2016-05-30 7:09 ` Razvan Cojocaru
2016-05-30 11:50 ` Jan Beulich
2016-05-30 19:47 ` Tamas K Lengyel
2016-05-30 20:20 ` Julien Grall
2016-05-30 20:37 ` Tamas K Lengyel
2016-05-30 20:46 ` Razvan Cojocaru
2016-05-30 20:53 ` Tamas K Lengyel
2016-05-30 21:35 ` Julien Grall
2016-05-30 21:41 ` Tamas K Lengyel
2016-05-31 7:54 ` Jan Beulich
2016-05-31 8:06 ` Razvan Cojocaru
2016-05-31 8:30 ` Jan Beulich
2016-05-31 16:20 ` Tamas K Lengyel
2016-05-31 7:48 ` Jan Beulich
2016-05-31 16:28 ` Tamas K Lengyel
2016-06-01 8:41 ` Jan Beulich
2016-06-01 11:24 ` Julien Grall
2016-06-01 18:21 ` Tamas K Lengyel
2016-06-01 19:34 ` Razvan Cojocaru
2016-06-01 19:43 ` Julien Grall
2016-06-02 7:35 ` Jan Beulich
2016-06-02 8:26 ` Razvan Cojocaru
2016-06-02 9:38 ` Jan Beulich [this message]
2016-06-02 9:42 ` Razvan Cojocaru
2016-06-01 19:38 ` Julien Grall
2016-06-01 19:49 ` Julien Grall
2016-06-01 19:50 ` Tamas K Lengyel
2016-05-29 22:37 ` [PATCH v4 6/8] tools/libxc: add xc_monitor_privileged_call Tamas K Lengyel
2016-05-29 22:37 ` [PATCH v4 7/8] tools/xen-access: add test-case for ARM SMC Tamas K Lengyel
2016-05-30 9:56 ` Wei Liu
2016-05-29 22:37 ` [PATCH v4 8/8] x86/vm_event: Add HVM debug exception vm_events Tamas K Lengyel
2016-05-30 7:29 ` Razvan Cojocaru
2016-05-30 14:16 ` Jan Beulich
2016-05-30 20:13 ` Tamas K Lengyel
2016-05-30 20:58 ` Andrew Cooper
2016-05-31 7:59 ` Jan Beulich
2016-06-01 21:46 ` Tamas K Lengyel
2016-06-01 22:17 ` Andrew Cooper
2016-06-02 0:01 ` Tamas K Lengyel
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