From: Borislav Petkov <bp@alien8.de>
To: shuo.a.liu@intel.com
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"H . Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
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>,
Dave Hansen <dave.hansen@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 12:54:08 +0200 [thread overview]
Message-ID: <20200930105408.GE6810@zn.tnic> (raw)
In-Reply-To: <20200922114311.38804-5-shuo.a.liu@intel.com>
On Tue, Sep 22, 2020 at 07:42:58PM +0800, shuo.a.liu@intel.com wrote:
> From: Shuo Liu <shuo.a.liu@intel.com>
>
> The Service VM communicates with the hypervisor via conventional
> hypercalls. VMCALL instruction is used to make the hypercalls.
>
> ACRN hypercall ABI:
> * Hypercall number is in R8 register.
> * Up to 2 parameters are in RDI and RSI registers.
> * Return value is in RAX register.
I'm assuming this is already cast in stone in the HV and it cannot be
changed?
> Introduce the ACRN hypercall interfaces. Because GCC doesn't support R8
> register as direct register constraints, here are two ways to use R8 in
> extended asm:
> 1) use explicit register variable as input
> 2) use supported constraint as input with a explicit MOV to R8 in
> beginning of asm
>
> The number of instructions of above two ways are same.
> Asm code from 1)
> 38: 41 b8 00 00 00 80 mov $0x80000000,%r8d
> 3e: 48 89 c7 mov %rax,%rdi
> 41: 0f 01 c1 vmcall
> Here, writes to the lower dword (%r8d) clear the upper dword of %r8 when
> the CPU is in 64-bit mode.
>
> Asm code from 2)
> 38: 48 89 c7 mov %rax,%rdi
> 3b: 49 b8 00 00 00 80 00 movabs $0x80000000,%r8
> 42: 00 00 00
> 45: 0f 01 c1 vmcall
>
> Choose 1) for code simplicity and a little bit of code size
> optimization.
What?
How much "optimization" is this actually? A couple of bytes?
And all that for this
/* Nothing can come between the r8 assignment and the asm: */
restriction?
If it is only a couple of bytes, just do the explicit MOV to %r8 and
f'get about it.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2020-09-30 10:54 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
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 [this message]
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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