From: Kai Huang <kai.huang@intel.com>
To: Dave Hansen <dave.hansen@intel.com>, Chao Gao <chao.gao@intel.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
seanjc@google.com, pbonzini@redhat.com, len.brown@intel.com,
tony.luck@intel.com, rafael.j.wysocki@intel.com,
reinette.chatre@intel.com, dan.j.williams@intel.com,
peterz@infradead.org, ak@linux.intel.com,
kirill.shutemov@linux.intel.com,
sathyanarayanan.kuppuswamy@linux.intel.com,
isaku.yamahata@intel.com, thomas.lendacky@amd.com,
Tianyu.Lan@microsoft.com
Subject: Re: [PATCH v5 04/22] x86/virt/tdx: Prevent ACPI CPU hotplug and ACPI memory hotplug
Date: Fri, 01 Jul 2022 10:45:24 +1200 [thread overview]
Message-ID: <dcdbadde527b4dc67efb5df64179fd1ec1bb073c.camel@intel.com> (raw)
In-Reply-To: <6abe32e1-51f8-a303-4ddb-2347dddcc960@intel.com>
On Thu, 2022-06-30 at 08:44 -0700, Dave Hansen wrote:
> On 6/29/22 16:02, Kai Huang wrote:
> > On Wed, 2022-06-29 at 07:22 -0700, Dave Hansen wrote:
> > > On 6/24/22 04:21, Kai Huang wrote:
> > > What does that #ifdef get us? I suspect you're back to trying to
> > > silence compiler warnings with #ifdefs. The compiler *knows* that it's
> > > only used in this file. It's also used all of once. If you make it
> > > 'static inline', you'll likely get the same code generation, no
> > > warnings, and don't need an #ifdef.
> >
> > The purpose is not to avoid warning, but to make intel_cc_platform_has(enum
> > cc_attr attr) simple that when neither TDX host and TDX guest code is turned on,
> > it can be simple:
> >
> > static bool intel_cc_platform_has(enum cc_attr attr)
> > {
> > return false;
> > }
> >
> > So I don't need to depend on how internal functions are implemented in the
> > header files and I don't need to guess how does compiler generate code.
>
> I hate to break it to you, but you actually need to know how the
> compiler works for you to be able to write good code. Ignoring all the
> great stuff that the compiler does for you makes your code worse.
Agreed.
>
> > And also because I personally believe it doesn't hurt readability.
>
> Are you saying that you're ignoring long-established kernel coding style
> conventions because of your personal beliefs? That seem, um, like an
> approach that's unlikely to help your code get accepted.
Agreed. Will keep this in mind. Thanks.
>
> > > The other option is to totally lean on the compiler to figure things
> > > out. Compile this program, then disassemble it and see what main() does.
> > >
> > > static void func(void)
> > > {
> > > printf("I am func()\n");
> > > }
> > >
> > > void main(int argc, char **argv)
> > > {
> > > if (0)
> > > func();
> > > }
> > >
> > > Then, do:
> > >
> > > - if (0)
> > > + if (argc)
> > >
> > > and run it again. What changed in the disassembly?
> >
> > You mean compile it again? I have to confess I never tried and don't know.
> > I'll try when I got some spare time. Thanks for the info.
>
> Yes, compile it again and run it again.
>
> But, seriously, it's a quick exercise. I can help make you some spare
> time if you wish. Just let me know.
So I tried. Took me less than 5 mins:)
The
if (0)
func();
never generates the code to actually call the func():
0000000000401137 <main>:
401137: 55 push %rbp
401138: 48 89 e5 mov %rsp,%rbp
40113b: 89 7d fc mov %edi,-0x4(%rbp)
40113e: 48 89 75 f0 mov %rsi,-0x10(%rbp)
401142: 90 nop
401143: 5d pop %rbp
401144: c3 ret
While
if (argc)
func();
generates the code to check argc and call func():
0000000000401137 <main>:
401137: 55 push %rbp
401138: 48 89 e5 mov %rsp,%rbp
40113b: 48 83 ec 10 sub $0x10,%rsp
40113f: 89 7d fc mov %edi,-0x4(%rbp)
401142: 48 89 75 f0 mov %rsi,-0x10(%rbp)
401146: 83 7d fc 00 cmpl $0x0,-0x4(%rbp)
40114a: 74 05 je 401151 <main+0x1a>
40114c: e8 d5 ff ff ff call 401126 <func>
401151: 90 nop
401152: c9 leave
401153: c3 ret
This is kinda no surprise.
Were you trying to make point that
if (false)
func();
doesn't generate any additional code?
I get your point now. Thanks :)
next prev parent reply other threads:[~2022-06-30 22:45 UTC|newest]
Thread overview: 114+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-22 11:15 [PATCH v5 00/22] TDX host kernel support Kai Huang
2022-06-22 11:15 ` [PATCH v5 01/22] x86/virt/tdx: Detect TDX during kernel boot Kai Huang
2022-06-23 5:57 ` Chao Gao
2022-06-23 9:23 ` Kai Huang
2022-08-02 2:01 ` [PATCH v5 1/22] " Wu, Binbin
2022-08-03 9:25 ` Kai Huang
2022-06-22 11:15 ` [PATCH v5 02/22] cc_platform: Add new attribute to prevent ACPI CPU hotplug Kai Huang
2022-06-22 11:42 ` Rafael J. Wysocki
2022-06-23 0:01 ` Kai Huang
2022-06-27 8:01 ` Igor Mammedov
2022-06-28 10:04 ` Kai Huang
2022-06-28 11:52 ` Igor Mammedov
2022-06-28 17:33 ` Rafael J. Wysocki
2022-06-28 23:41 ` Kai Huang
2022-06-24 18:57 ` Dave Hansen
2022-06-27 5:05 ` Kai Huang
2022-07-13 11:09 ` Kai Huang
2022-07-19 17:46 ` Dave Hansen
2022-07-19 23:54 ` Kai Huang
2022-08-03 3:40 ` Binbin Wu
2022-08-03 9:20 ` Kai Huang
2022-06-29 5:33 ` Christoph Hellwig
2022-06-29 9:09 ` Kai Huang
2022-08-03 3:55 ` Binbin Wu
2022-08-03 9:21 ` Kai Huang
2022-06-22 11:15 ` [PATCH v5 03/22] cc_platform: Add new attribute to prevent ACPI memory hotplug Kai Huang
2022-06-22 11:45 ` Rafael J. Wysocki
2022-06-23 0:08 ` Kai Huang
2022-06-28 17:55 ` Rafael J. Wysocki
2022-06-28 12:01 ` Igor Mammedov
2022-06-28 23:49 ` Kai Huang
2022-06-29 8:48 ` Igor Mammedov
2022-06-29 9:13 ` Kai Huang
2022-06-22 11:16 ` [PATCH v5 04/22] x86/virt/tdx: Prevent ACPI CPU hotplug and " Kai Huang
2022-06-24 1:41 ` Chao Gao
2022-06-24 11:21 ` Kai Huang
2022-06-29 8:35 ` Yuan Yao
2022-06-29 9:17 ` Kai Huang
2022-06-29 14:22 ` Dave Hansen
2022-06-29 23:02 ` Kai Huang
2022-06-30 15:44 ` Dave Hansen
2022-06-30 22:45 ` Kai Huang [this message]
2022-06-22 11:16 ` [PATCH v5 05/22] x86/virt/tdx: Prevent hot-add driver managed memory Kai Huang
2022-06-24 2:12 ` Chao Gao
2022-06-24 11:23 ` Kai Huang
2022-06-24 19:01 ` Dave Hansen
2022-06-27 5:27 ` Kai Huang
2022-06-22 11:16 ` [PATCH v5 06/22] x86/virt/tdx: Add skeleton to initialize TDX on demand Kai Huang
2022-06-24 2:39 ` Chao Gao
2022-06-24 11:27 ` Kai Huang
2022-06-22 11:16 ` [PATCH v5 07/22] x86/virt/tdx: Implement SEAMCALL function Kai Huang
2022-06-24 18:38 ` Dave Hansen
2022-06-27 5:23 ` Kai Huang
2022-06-27 20:58 ` Dave Hansen
2022-06-27 22:10 ` Kai Huang
2022-07-19 19:39 ` Dan Williams
2022-07-19 23:28 ` Kai Huang
2022-07-20 10:18 ` Kai Huang
2022-07-20 16:48 ` Dave Hansen
2022-07-21 1:52 ` Kai Huang
2022-07-27 0:34 ` Kai Huang
2022-07-27 0:50 ` Dave Hansen
2022-07-27 12:46 ` Kai Huang
2022-08-03 2:37 ` Kai Huang
2022-08-03 14:20 ` Dave Hansen
2022-08-03 22:35 ` Kai Huang
2022-08-04 10:06 ` Kai Huang
2022-06-22 11:16 ` [PATCH v5 08/22] x86/virt/tdx: Shut down TDX module in case of error Kai Huang
2022-06-24 18:50 ` Dave Hansen
2022-06-27 5:26 ` Kai Huang
2022-06-27 20:46 ` Dave Hansen
2022-06-27 22:34 ` Kai Huang
2022-06-27 22:56 ` Dave Hansen
2022-06-27 23:59 ` Kai Huang
2022-06-28 0:03 ` Dave Hansen
2022-06-28 0:11 ` Kai Huang
2022-06-22 11:16 ` [PATCH v5 09/22] x86/virt/tdx: Detect TDX module by doing module global initialization Kai Huang
2022-06-22 11:16 ` [PATCH v5 10/22] x86/virt/tdx: Do logical-cpu scope TDX module initialization Kai Huang
2022-06-22 11:17 ` [PATCH v5 11/22] x86/virt/tdx: Get information about TDX module and TDX-capable memory Kai Huang
2022-06-22 11:17 ` [PATCH v5 12/22] x86/virt/tdx: Convert all memory regions in memblock to TDX memory Kai Huang
2022-06-24 19:40 ` Dave Hansen
2022-06-27 6:16 ` Kai Huang
2022-07-07 2:37 ` Kai Huang
2022-07-07 14:26 ` Dave Hansen
2022-07-07 14:36 ` Juergen Gross
2022-07-07 23:42 ` Kai Huang
2022-07-07 23:34 ` Kai Huang
2022-08-03 1:30 ` Kai Huang
2022-08-03 14:22 ` Dave Hansen
2022-08-03 22:14 ` Kai Huang
2022-06-22 11:17 ` [PATCH v5 13/22] x86/virt/tdx: Add placeholder to construct TDMRs based on memblock Kai Huang
2022-06-22 11:17 ` [PATCH v5 14/22] x86/virt/tdx: Create TDMRs to cover all memblock memory regions Kai Huang
2022-06-22 11:17 ` [PATCH v5 15/22] x86/virt/tdx: Allocate and set up PAMTs for TDMRs Kai Huang
2022-06-24 20:13 ` Dave Hansen
2022-06-27 10:31 ` Kai Huang
2022-06-27 20:41 ` Dave Hansen
2022-06-27 22:50 ` Kai Huang
2022-06-27 22:57 ` Dave Hansen
2022-06-27 23:05 ` Kai Huang
2022-06-28 0:48 ` Xiaoyao Li
2022-06-28 17:03 ` Dave Hansen
2022-08-17 22:46 ` Sagi Shahar
2022-08-17 23:43 ` Huang, Kai
2022-06-22 11:17 ` [PATCH v5 16/22] x86/virt/tdx: Set up reserved areas for all TDMRs Kai Huang
2022-06-22 11:17 ` [PATCH v5 17/22] x86/virt/tdx: Reserve TDX module global KeyID Kai Huang
2022-06-22 11:17 ` [PATCH v5 18/22] x86/virt/tdx: Configure TDX module with TDMRs and " Kai Huang
2022-06-22 11:17 ` [PATCH v5 19/22] x86/virt/tdx: Configure global KeyID on all packages Kai Huang
2022-06-22 11:17 ` [PATCH v5 20/22] x86/virt/tdx: Initialize all TDMRs Kai Huang
2022-06-22 11:17 ` [PATCH v5 21/22] x86/virt/tdx: Support kexec() Kai Huang
2022-06-22 11:17 ` [PATCH v5 22/22] Documentation/x86: Add documentation for TDX host support Kai Huang
2022-08-18 4:07 ` Bagas Sanjaya
2022-08-18 9:33 ` Huang, Kai
2022-06-24 19:47 ` [PATCH v5 00/22] TDX host kernel support Dave Hansen
2022-06-27 4:09 ` Kai Huang
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