linux-kernel - Re: [RFC PATCH 2/3] x86/cpufeatures: Combine word 11 and 12 into new scattered features word 11

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Date:   Fri, 14 Jun 2019 13:44:10 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>,
        Christopherson Sean J <sean.j.christopherson@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [RFC PATCH 2/3] x86/cpufeatures: Combine word 11 and 12 into new
 scattered features word 11

On Thu, Jun 13, 2019 at 01:51:03PM -0700, Fenghua Yu wrote:
> It's a waste for the four X86_FEATURE_CQM_* features to occupy two
> pure feature bits words. To better utilize feature words, re-define
> word 11 to host scattered features and move the four X86_FEATURE_CQM_*
> features into word 11. More scattered features can be added in word 11
> in the future.
> 
> KVM doesn't support resctrl now. So it's safe to move the
> X86_FEATURE_CQM_* features to scattered features word 11 for KVM.
> 
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>

...

> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index 9a327d5b6d1f..d78a61408243 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -47,8 +47,6 @@ static const struct cpuid_reg reverse_cpuid[] = {
>  	[CPUID_8000_0001_ECX] = {0x80000001, 0, CPUID_ECX},
>  	[CPUID_7_0_EBX]       = {         7, 0, CPUID_EBX},
>  	[CPUID_D_1_EAX]       = {       0xd, 1, CPUID_EAX},
> -	[CPUID_F_0_EDX]       = {       0xf, 0, CPUID_EDX},
> -	[CPUID_F_1_EDX]       = {       0xf, 1, CPUID_EDX},

I think you're going to have to change those to:

        [CPUID_LNX_4]         = {         0, 0, 0},
        [CPUID_7_1_EAX]       = {         7, 1, CPUID_EAX },

instead of removing them because kvm is basically hardcoding the feature
words and then bitches when array elements in the middle get removed:

In file included from ./include/linux/export.h:45,
                 from ./include/linux/linkage.h:7,
                 from ./include/linux/preempt.h:10,
                 from ./include/linux/hardirq.h:5,
                 from ./include/linux/kvm_host.h:10,
                 from arch/x86/kvm/x86.c:22:
In function ‘x86_feature_cpuid’,
    inlined from ‘guest_cpuid_get_register’ at arch/x86/kvm/cpuid.h:71:33,
    inlined from ‘guest_cpuid_has’ at arch/x86/kvm/cpuid.h:100:8,
    inlined from ‘kvm_get_msr_common’ at arch/x86/kvm/x86.c:2804:8:
./include/linux/compiler.h:345:38: error: call to ‘__compiletime_assert_62’ declared with attribute error: BUILD_BUG_ON failed: x86_leaf >= ARRAY_SIZE(reverse_cpuid)
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
                                      ^
./include/linux/compiler.h:326:4: note: in definition of macro ‘__compiletime_assert’
    prefix ## suffix();    \
    ^~~~~~
./include/linux/compiler.h:345:2: note: in expansion of macro ‘_compiletime_assert’
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
  ^~~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’
 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                     ^~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:50:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
  BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
  ^~~~~~~~~~~~~~~~
arch/x86/kvm/cpuid.h:62:2: note: in expansion of macro ‘BUILD_BUG_ON’
  BUILD_BUG_ON(x86_leaf >= ARRAY_SIZE(reverse_cpuid));
  ^~~~~~~~~~~~
./include/linux/compiler.h:345:38: error: call to ‘__compiletime_assert_63’ declared with attribute error: BUILD_BUG_ON failed: reverse_cpuid[x86_leaf].function == 0
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
                                      ^
./include/linux/compiler.h:326:4: note: in definition of macro ‘__compiletime_assert’
    prefix ## suffix();    \
    ^~~~~~
./include/linux/compiler.h:345:2: note: in expansion of macro ‘_compiletime_assert’
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
  ^~~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’
 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                     ^~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:50:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
  BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
  ^~~~~~~~~~~~~~~~
arch/x86/kvm/cpuid.h:63:2: note: in expansion of macro ‘BUILD_BUG_ON’
  BUILD_BUG_ON(reverse_cpuid[x86_leaf].function == 0);
  ^~~~~~~~~~~~
make[2]: *** [scripts/Makefile.build:278: arch/x86/kvm/x86.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [scripts/Makefile.build:489: arch/x86/kvm] Error 2
make[1]: *** Waiting for unfinished jobs....
make: *** [Makefile:1071: arch/x86] Error 2
make: *** Waiting for unfinished jobs....

-- 
Regards/Gruss,
    Boris.

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