Re: [PATCH 11/16] x86/cpu: Print VMX features as separate line item in /proc/cpuinfo

From: Jim Mattson <jmattson@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Sean Christopherson" <sean.j.christopherson@intel.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Arnaldo Carvalho de Melo" <acme@kernel.org>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Tony Luck" <tony.luck@intel.com>,
	"Tony W Wang-oc" <TonyWWang-oc@zhaoxin.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Alexander Shishkin" <alexander.shishkin@linux.intel.com>,
	"Jiri Olsa" <jolsa@redhat.com>,
	"Namhyung Kim" <namhyung@kernel.org>,
	"Vitaly Kuznetsov" <vkuznets@redhat.com>,
	"Wanpeng Li" <wanpengli@tencent.com>,
	"Joerg Roedel" <joro@8bytes.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"kvm list" <kvm@vger.kernel.org>,
	linux-edac@vger.kernel.org, "Borislav Petkov" <bp@suse.de>,
	"Jarkko Sakkinen" <jarkko.sakkinen@linux.intel.com>
Subject: Re: [PATCH 11/16] x86/cpu: Print VMX features as separate line item in /proc/cpuinfo
Date: Tue, 8 Oct 2019 09:53:44 -0700	[thread overview]
Message-ID: <CALMp9eSM=rq+jEEzPwWNHNxv03F1s2Dysa7euWJ==PaE=b1sMw@mail.gmail.com> (raw)
In-Reply-To: <bd2cffea-6427-b3cc-7098-a881e3d4522d@redhat.com>

On Mon, Oct 7, 2019 at 11:57 PM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 07/10/19 21:56, Sean Christopherson wrote:
> > On Mon, Oct 07, 2019 at 07:12:37PM +0200, Paolo Bonzini wrote:
> >> On 04/10/19 23:56, Sean Christopherson wrote:
> >>> diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
> >>> index cb2e49810d68..4eec8889b0ff 100644
> >>> --- a/arch/x86/kernel/cpu/proc.c
> >>> +++ b/arch/x86/kernel/cpu/proc.c
> >>> @@ -7,6 +7,10 @@
> >>>
> >>>  #include "cpu.h"
> >>>
> >>> +#ifdef CONFIG_X86_VMX_FEATURE_NAMES
> >>> +extern const char * const x86_vmx_flags[NVMXINTS*32];
> >>> +#endif
> >>> +
> >>>  /*
> >>>   * Get CPU information for use by the procfs.
> >>>   */
> >>> @@ -102,6 +106,17 @@ static int show_cpuinfo(struct seq_file *m, void *v)
> >>>             if (cpu_has(c, i) && x86_cap_flags[i] != NULL)
> >>>                     seq_printf(m, " %s", x86_cap_flags[i]);
> >>
> >> I'm afraid this is going to break some scripts in the wild.  I would
> >> simply remove the seq_puts below.
> >
> > Can you elaborate?  I'm having trouble connecting the dots...
>
> Somebody is bound to have scripts doing "grep ^flags.*ept /proc/cpuinfo"
> or checking for VMX flags under some kind of "if (/^flags/)", so it's
> safer not to separate VMX and non-VMX flags.

Yep. Not quite that exact syntax, but we do have, e.g.:

./x86/feature_check.sh ept

...and you can imagine what feature_check.sh does.