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Re: [Xen-devel] [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
- To: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
- From: Waiman Long <longman@xxxxxxxxxx>
- Date: Tue, 14 Feb 2017 09:46:17 -0500
- Cc: linux-arch@xxxxxxxxxxxxxxx, Juergen Gross <jgross@xxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, x86@xxxxxxxxxx, kvm@xxxxxxxxxxxxxxx, Radim Krčmář <rkrcmar@xxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Pan Xinhui <xinhui.pan@xxxxxxxxxxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx, Chris Wright <chrisw@xxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Alok Kataria <akataria@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>
- Delivery-date: Tue, 14 Feb 2017 14:46:33 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On 02/14/2017 04:39 AM, Peter Zijlstra wrote:
> On Mon, Feb 13, 2017 at 05:34:01PM -0500, Waiman Long wrote:
>> It is the address of &steal_time that will exceed the 32-bit limit.
> That seems extremely unlikely. That would mean we have more than 4G
> worth of per-cpu variables declared in the kernel.
I have some doubt about if the compiler is able to properly use
RIP-relative addressing for this. Anyway, it seems like constraints
aren't allowed for asm() when not in the function context, at least for
the the compiler that I am using (4.8.5). So it is a moot point.
Cheers,
Longman
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