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From: Peter Zijlstra <peterz@infradead.org>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	shuo.a.liu@intel.com, linux-kernel@vger.kernel.org,
	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>,
	segher@kernel.crashing.org, ndesaulniers@google.com
Subject: Re: [PATCH v4 04/17] x86/acrn: Introduce hypercall interfaces
Date: Wed, 30 Sep 2020 13:16:12 +0200	[thread overview]
Message-ID: <20200930111612.GZ2628@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <6f9a2b83-6904-2290-6c4f-526672390beb@intel.com>

On Sun, Sep 27, 2020 at 08:38:03AM -0700, Dave Hansen wrote:
> On 9/27/20 3:51 AM, Greg Kroah-Hartman wrote:
> >> +static inline long acrn_hypercall0(unsigned long hcall_id)
> >> +{
> >> +	register long r8 asm("r8");
> >> +	long result;
> >> +
> >> +	/* Nothing can come between the r8 assignment and the asm: */
> >> +	r8 = hcall_id;
> >> +	asm volatile("vmcall\n\t"
> >> +		     : "=a" (result)
> >> +		     : "r" (r8)
> >> +		     : );
> > What keeps an interrupt from happening between the r8 assignment and the
> > asm: ?
> 
> It's probably better phrased something like: "No other C code can come
> between this r8 assignment and the inline asm".  An interrupt would
> actually be fine in there because interrupts save and restore all
> register state, including r8.
> 
> The problem (mentioned in the changelog) is that gcc does not let you
> place data directly into r8.  But, it does allow you to declare a
> register variable that you can assign to use r8.  There might be a
> problem if a function calls was in between and clobber the register,
> thus the "nothing can come between" comment.
> 
> The comment is really intended to scare away anyone from adding printk()'s.
> 
> More information about these register variables is here:
> 
> > https://gcc.gnu.org/onlinedocs/gcc/Local-Register-Variables.html#Local-Register-Variables
> 
> Any better ideas for comments would be greatly appreciated.  It has 4 or
> 5 copies so I wanted it to be succinct.

This is disguisting.. Segher, does this actually work? Nick, does clang
also support this?


  reply	other threads:[~2020-09-30 11:16 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 [this message]
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
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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