linux-kernel - Re: [tip:x86/mm] x86/tme: Detect if TME and MKTME is activated by BIOS

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Message-ID: <1520978865.13820.3.camel@linux.intel.com>
Date:   Wed, 14 Mar 2018 11:07:45 +1300
From:   Kai Huang <kai.huang@...ux.intel.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     dave.hansen@...el.com, peterz@...radead.org, hpa@...or.com,
        mingo@...nel.org, linux-kernel@...r.kernel.org, tglx@...utronix.de,
        torvalds@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
        thomas.lendacky@....com, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/mm] x86/tme: Detect if TME and MKTME is activated by
 BIOS

On Tue, 2018-03-13 at 15:49 +0300, Kirill A. Shutemov wrote:
> On Tue, Mar 13, 2018 at 03:12:02PM +1300, Kai Huang wrote:
> > It seems setup_pku() will call get_cpu_cap to restore c-
> > >x86_phys_bits
> > later? In which case I think you need to change setup_pku as well.
> 
> Thanks for catching this.
> 
> I think setup_pku() shouldn't call get_cpu_cap().
> 
> Any objections against this:
> 
> diff --git a/arch/x86/kernel/cpu/common.c
> b/arch/x86/kernel/cpu/common.c
> index 348cf4821240..ce10d8ae4cd6 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -362,6 +362,8 @@ static bool pku_disabled;
> 
>  static __always_inline void setup_pku(struct cpuinfo_x86 *c)
>  {
> +       u32 eax, ebx, ecx, edx;
> +
>         /* check the boot processor, plus compile options for PKU: */
>         if (!cpu_feature_enabled(X86_FEATURE_PKU))
>                 return;
> @@ -377,7 +379,8 @@ static __always_inline void setup_pku(struct
> cpuinfo_x86 *c)
>          * cpuid bit to be set.  We need to ensure that we
>          * update that bit in this CPU's "cpu_info".
>          */
> -       get_cpu_cap(c);
> +       cpuid_count(0x00000007, 0, &eax, &ebx, &ecx, &edx);
> +       c->x86_capability[CPUID_7_ECX] = ecx;
>  }
> 
>  #ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
> 
> > And for the comments here, I think it can be refined. It is true
> > that
> > VM guest needs to know bits of physical address, but this info is
> > not
> > used only by VM. I think the reason we need to update is this is
> > simply
> > the fact.
> 
> Fair enough. Like this?

Yes good to me. Thanks.

Thanks,
-Kai
> 
> diff --git a/arch/x86/kernel/cpu/intel.c
> b/arch/x86/kernel/cpu/intel.c
> index e8ddc6dcfd53..ac45ba7398d9 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -612,11 +612,8 @@ static void detect_tme(struct cpuinfo_x86 *c)
>  #endif
> 
>         /*
> -        * Exclude KeyID bits from physical address bits.
> -        *
> -        * We have to do this even if we are not going to use KeyID
> bits
> -        * ourself. VM guests still have to know that these bits are
> not usable
> -        * for physical address.
> +        * KeyID bits effectively lower number of physical address
> bits.
> +        * Let's update cpuinfo_x86::x86_phys_bits to reflect the
> fact.
>          */
>         c->x86_phys_bits -= keyid_bits;
>  }