linux-kernel - Re: [Patch v2 2/2] amd: uncore: Get correct number of cores sharing last level cache

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20170611175106.zeldukujqmxe2gt2@pd.tnic>
Date:   Sun, 11 Jun 2017 19:51:06 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Janakarajan Natarajan <Janakarajan.Natarajan@....com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Subject: Re: [Patch v2 2/2] amd: uncore: Get correct number of cores sharing
 last level cache

On Thu, Jun 08, 2017 at 02:48:24PM -0500, Janakarajan Natarajan wrote:
> In Family 17h, the number of cores sharing a cache level is obtained
> from the Cache Properties CPUID leaf (0x8000001d) by passing in the
> cache level in ECX. In prior families, a cache level of 2 was used to
> determine this information.
> 
> To get the right information, irrespective of Family, iterate over
> the cache levels using CPUID 0x8000001d. The last level cache is the
> last value to return a non-zero value in EAX.
> 
> Signed-off-by: Janakarajan Natarajan <Janakarajan.Natarajan@....com>
> ---
>  arch/x86/events/amd/uncore.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/events/amd/uncore.c b/arch/x86/events/amd/uncore.c
> index e34f8a6..6952262 100644
> --- a/arch/x86/events/amd/uncore.c
> +++ b/arch/x86/events/amd/uncore.c
> @@ -400,11 +400,22 @@ static int amd_uncore_cpu_starting(unsigned int cpu)
>  
>  	if (amd_uncore_llc) {
>  		unsigned int apicid = cpu_data(cpu).apicid;
> -		unsigned int nshared;
> +		unsigned int nshared, cache_topology, prev_eax = 0;

cache_topology is too long and not really what it is. Simply call it
subleaf.

>  		uncore = *per_cpu_ptr(amd_uncore_llc, cpu);
> -		cpuid_count(0x8000001d, 2, &eax, &ebx, &ecx, &edx);
> -		nshared = ((eax >> 14) & 0xfff) + 1;

<---- newline here.

> +		/*
> +		 * Iterate over Cache Topology Definition leaves until no
> +		 * more cache descriptions are available
							^
							|
All sentences need to end with a fullstop.--------------+

> +		 */
> +		for(cache_topology = 0; cache_topology < 5; cache_topology++) {
> +			cpuid_count(0x8000001d, cache_topology, &eax, &ebx, &ecx, &edx);
> +
> +			if ((eax & 0x1f) == 0) /* EAX[0:4] gives type of cache */

No side comments, put it over the if-line.

Also, we generally do 0-tests this way:

			if (!(eax & 0x1f))

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.