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From: Segher Boessenkool <segher@kernel.crashing.org>
To: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Dave Hansen <dave.hansen@intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	shuo.a.liu@intel.com, LKML <linux-kernel@vger.kernel.org>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	Yu Wang <yu1.wang@intel.com>,
	Reinette Chatre <reinette.chatre@intel.com>,
	Yakui Zhao <yakui.zhao@intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Fengwei Yin <fengwei.yin@intel.com>,
	Zhi Wang <zhi.a.wang@intel.com>,
	Zhenyu Wang <zhenyuw@linux.intel.com>
Subject: Re: [PATCH v4 04/17] x86/acrn: Introduce hypercall interfaces
Date: Wed, 30 Sep 2020 19:08:32 -0500	[thread overview]
Message-ID: <20201001000832.GE28786@gate.crashing.org> (raw)
In-Reply-To: <20200930195915.GA3180913@rani.riverdale.lan>

On Wed, Sep 30, 2020 at 03:59:15PM -0400, Arvind Sankar wrote:
> On Wed, Sep 30, 2020 at 12:14:03PM -0700, Nick Desaulniers wrote:
> > On Wed, Sep 30, 2020 at 10:13 AM Peter Zijlstra <peterz@infradead.org> wrote:
> > >
> > > On Wed, Sep 30, 2020 at 11:10:36AM -0500, Segher Boessenkool wrote:
> > >
> > > > Since this variable is a local register asm, on entry to the asm the
> > > > compiler guarantees that the value lives in the assigned register (the
> > > > "r8" hardware register in this case).  This all works completely fine.
> > > > This is the only guaranteed behaviour for local register asm (well,
> > > > together with analogous behaviour for outputs).
> 
> How strict is the guarantee? This is an inline function -- could the
> compiler decide to reorder some other code in between the r8 assignment
> and the asm statement when it gets inlined?

Nope.  It will be in r8 on entry to the asm.  A guarantee is a
guarantee; it is not a "yeah maybe, we'll see".

> > Do we need register local storage here?
> > 
> > static inline long bar(unsigned long hcall_id)
> > {
> >   long result;
> >   asm volatile("movl %1, %%r8d\n\t"
> >   "vmcall\n\t"
> >     : "=a" (result)
> >     : "ir" (hcall_id)
> >     : );
> >   return result;
> > }
> 
> This seems more robust, though you probably need an r8 clobber in there?

Oh, x86 has the operand order inverted, so this should work in fact.


Segher

  parent reply	other threads:[~2020-10-01  0:16 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-22 11:42 [PATCH v4 00/17] HSM driver for ACRN hypervisor shuo.a.liu
2020-09-22 11:42 ` [PATCH v4 01/17] docs: acrn: Introduce ACRN shuo.a.liu
2020-10-09  1:48   ` Randy Dunlap
2020-10-12  8:50     ` Shuo A Liu
2020-09-22 11:42 ` [PATCH v4 02/17] x86/acrn: Introduce acrn_{setup, remove}_intr_handler() shuo.a.liu
2020-09-27 10:49   ` Greg Kroah-Hartman
2020-09-28  3:28     ` Shuo A Liu
2020-09-29 18:01   ` Borislav Petkov
2020-09-29 20:07     ` Thomas Gleixner
2020-09-29 20:26       ` Borislav Petkov
2020-09-30  3:02         ` Shuo A Liu
2020-09-22 11:42 ` [PATCH v4 03/17] x86/acrn: Introduce an API to check if a VM is privileged shuo.a.liu
2020-09-30  8:09   ` Borislav Petkov
2020-10-12  8:40     ` Shuo A Liu
2020-09-22 11:42 ` [PATCH v4 04/17] x86/acrn: Introduce hypercall interfaces shuo.a.liu
2020-09-27 10:51   ` Greg Kroah-Hartman
2020-09-27 10:53     ` Greg Kroah-Hartman
2020-09-28  3:38       ` Shuo A Liu
2020-09-27 15:38     ` Dave Hansen
2020-09-30 11:16       ` Peter Zijlstra
2020-09-30 16:10         ` Segher Boessenkool
2020-09-30 17:13           ` Peter Zijlstra
2020-09-30 19:14             ` Nick Desaulniers
2020-09-30 19:42               ` Peter Zijlstra
2020-09-30 23:58                 ` Segher Boessenkool
2020-09-30 19:59               ` Arvind Sankar
2020-09-30 20:01                 ` Arvind Sankar
2020-10-01  0:08                 ` Segher Boessenkool [this message]
2020-09-30 23:25               ` Segher Boessenkool
2020-09-30 23:38                 ` Arvind Sankar
2020-10-01  0:11                   ` Segher Boessenkool
2020-10-12  8:44               ` Shuo A Liu
2020-10-12 16:49                 ` Arvind Sankar
2020-10-13  2:44                   ` Shuo A Liu
2020-09-30 10:54   ` Borislav Petkov
2020-10-12  8:49     ` Shuo A Liu
2020-09-22 11:42 ` [PATCH v4 05/17] virt: acrn: Introduce ACRN HSM basic driver shuo.a.liu
2020-09-22 11:43 ` [PATCH v4 08/17] virt: acrn: Introduce EPT mapping management shuo.a.liu
2020-09-22 11:43 ` [PATCH v4 10/17] virt: acrn: Introduce PCI configuration space PIO accesses combiner shuo.a.liu
2020-09-22 11:43 ` [PATCH v4 11/17] virt: acrn: Introduce interfaces for PCI device passthrough shuo.a.liu
2020-09-22 11:43 ` [PATCH v4 12/17] virt: acrn: Introduce interrupt injection interfaces shuo.a.liu
2020-09-22 11:43 ` [PATCH v4 14/17] virt: acrn: Introduce I/O ranges operation interfaces shuo.a.liu
2020-09-22 11:43 ` [PATCH v4 16/17] virt: acrn: Introduce irqfd shuo.a.liu
2020-09-22 11:43 ` [PATCH v4 17/17] virt: acrn: Introduce an interface for Service VM to control vCPU shuo.a.liu
2020-09-27 10:44   ` Greg Kroah-Hartman
2020-09-28  4:10     ` Shuo A Liu
2020-09-28  5:23       ` Greg Kroah-Hartman
2020-09-28  6:33         ` Shuo A Liu
2020-09-27  0:24 ` [PATCH v4 00/17] HSM driver for ACRN hypervisor Liu, Shuo A
2020-09-27  5:42   ` Greg Kroah-Hartman
     [not found] ` <20200922114311.38804-7-shuo.a.liu@intel.com>
2020-09-27 10:45   ` [PATCH v4 06/17] virt: acrn: Introduce VM management interfaces Greg Kroah-Hartman
2020-09-28  3:43     ` Shuo A Liu
2020-09-27 10:47   ` Greg Kroah-Hartman
2020-09-28  3:50     ` Shuo A Liu
2020-09-28  5:25       ` Greg Kroah-Hartman
2020-09-28  6:29         ` Shuo A Liu
2020-09-28 12:26           ` Greg Kroah-Hartman
2020-09-30  2:49             ` Shuo A Liu

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