From: Jan Kiszka <jan.kiszka@siemens.com>
To: Avi Kivity <avi@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: Re: [PATCH 04/19] qemu-kvm: x86: Drop MSR reset
Date: Thu, 05 May 2011 11:32:26 +0200 [thread overview]
Message-ID: <4DC26EAA.7080803@siemens.com> (raw)
In-Reply-To: <4DC265A5.90301@redhat.com>
On 2011-05-05 10:53, Avi Kivity wrote:
> On 05/05/2011 11:44 AM, Jan Kiszka wrote:
>> On 2011-05-05 10:33, Avi Kivity wrote:
>> > On 05/05/2011 11:27 AM, Jan Kiszka wrote:
>> >>>
>> >>> 1. Call KVM_CREATE_VCPU. This causes all MSRs to be initialized to
>> >>> their power-on reset values.
>> >>
>> >> Almost all: Which ones are CPU specific like the APIC_BASE?
>> >
>> > Do you mean cpu specific as in smp or cpu specific as in cpu model?
>>
>> Yep.
>
> Doh.
>
>> >
>> > If the former, we simply do the reset operation per-cpu. It's the
>> > natural thing anyway.
>>
>> Quite wasteful /wrt to memory given that the majority will be identical.
>
> We're talking a few hundred bytes per cpu. If you want to save memory,
> look at the PhysPageDesc array, it takes up 0.4% of guest memory, so 4MB
> for a 1GB guest.
I know (that's fixable, BTW). But that should not excuse needless memory
wasting elsewhere.
>
>> >> Nevertheless, the qemu-kvm code is already unneeded today and can
>> safely
>> >> be removed IMHO.
>> >
>> > I don't follow? Won't it cause a regression?
>>
>> Not at all. We use the "individual care" pattern upstream now,
>> specifically for those MSRs (kvmclock) for which the qemu-kvm code was
>> introduced.
>
> I mean a future regression with current+patch qemu and a new kernel.
For sane scenarios, such a combination should never expose new (ie.
unknown from qemu's POV) MSRs to the guest. Thus not clearing them
cannot cause any harm.
BTW, you also do not know if 0 will be the right reset value for these
to-be-invented MSRs. That could cause regression as well.
>
>> >
>> > Of course, if we get a patch soon no one will ever see the
>> regression so
>> > we can apply the series.
>>
>> I will still require the usual testing and merging round via upstream
>> and back. Not sure when I'll be able to work on it, probably not the
>> next days.
>
> If you can do it within a couple of weeks or so that should be fine.
>
We'll see, but I still do not share your concern regarding future
regressions when removing the fragile reset code.
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
next prev parent reply other threads:[~2011-05-05 9:32 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-04 19:43 [PATCH 00/19] qemu-kvm: Cleanup and switch to upstream - Part I Jan Kiszka
2011-05-04 19:43 ` [PATCH 01/19] qemu-kvm: Switch to upstream mp_state functions Jan Kiszka
2011-05-04 19:43 ` [PATCH 02/19] qemu-kvm: x86: Use upstream kvmclock device Jan Kiszka
2011-05-04 19:43 ` [PATCH 03/19] Revert "introduce VMSTATE_U64" Jan Kiszka
2011-05-04 19:43 ` [PATCH 04/19] qemu-kvm: x86: Drop MSR reset Jan Kiszka
2011-05-05 8:08 ` Avi Kivity
2011-05-05 8:11 ` Jan Kiszka
2011-05-05 8:16 ` Avi Kivity
2011-05-05 8:27 ` Jan Kiszka
2011-05-05 8:33 ` Avi Kivity
2011-05-05 8:44 ` Jan Kiszka
2011-05-05 8:53 ` Avi Kivity
2011-05-05 9:32 ` Jan Kiszka [this message]
2011-05-05 10:22 ` Avi Kivity
2011-05-05 10:36 ` Jan Kiszka
2011-05-05 11:57 ` Avi Kivity
2011-05-05 11:22 ` Gleb Natapov
2011-05-05 11:58 ` Avi Kivity
2011-05-05 12:23 ` Gleb Natapov
2011-05-05 12:42 ` Jan Kiszka
2011-05-05 13:33 ` Marcelo Tosatti
2011-05-05 18:08 ` Gleb Natapov
2011-05-04 19:43 ` [PATCH 05/19] qemu-kvm: Use upstream VCPU reset services Jan Kiszka
2011-05-04 19:43 ` [PATCH 06/19] qemu-kvm: Use upstream vcpu initialization Jan Kiszka
2011-05-04 19:43 ` [PATCH 07/19] qemu-kvm: Start using qemu-thread services Jan Kiszka
2011-05-04 19:43 ` [PATCH 08/19] qemu-kvm: Use upstream kvm_arch_get/put_registers Jan Kiszka
2011-05-04 19:43 ` [PATCH 09/19] qemu-kvm: Use upstream state synchronization services Jan Kiszka
2011-05-04 19:43 ` [PATCH 10/19] qemu-kvm: Drop remaining libkvm fragments Jan Kiszka
2011-05-04 19:43 ` [PATCH 11/19] qemu-kvm: Drop some more unused code Jan Kiszka
2011-05-04 19:43 ` [PATCH 12/19] qemu-kvm: Drop some obsolete/unused fields from kvm_context Jan Kiszka
2011-05-04 19:43 ` [PATCH 13/19] qemu-kvm: Refactor in-kernel irqchip and pit control Jan Kiszka
2011-05-04 19:43 ` [PATCH 14/19] qemu-kvm: Fold kvm_create into kvm_create_context Jan Kiszka
2011-05-04 19:43 ` [PATCH 15/19] qemu-kvm: Fold kvm_arch_qemu_create_context into kvm_arch_create Jan Kiszka
2011-05-04 19:43 ` [PATCH 16/19] qemu-kvm: Push PIT reinjection control into x86 code Jan Kiszka
2011-05-04 19:43 ` [PATCH 17/19] qemu-kvm: Replace kvm_show_regs/code with cpu_dump_state Jan Kiszka
2011-05-04 19:43 ` [PATCH 18/19] qemu-kvm: Fold kvm_init_coalesced_mmio into kvm_create_context Jan Kiszka
2011-05-04 19:43 ` [PATCH 19/19] qemu-kvm: x86: Use kvm_arch_init Jan Kiszka
2011-05-05 8:22 ` [PATCH 00/19] qemu-kvm: Cleanup and switch to upstream - Part I Avi Kivity
2011-05-05 8:29 ` Jan Kiszka
2011-05-06 13:51 ` Marcelo Tosatti
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=4DC26EAA.7080803@siemens.com \
--to=jan.kiszka@siemens.com \
--cc=avi@redhat.com \
--cc=kvm@vger.kernel.org \
--cc=mtosatti@redhat.com \
/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