linux-kernel - Re: [PATCH] ACPI: processor_idle: Skip dummy wait for processors based on the Zen microarchitecture

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

Message-ID: <2b6143b6-9db4-05bc-1e8d-c5d129126f99@intel.com>
Date:   Wed, 21 Sep 2022 07:15:07 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     K Prateek Nayak <kprateek.nayak@....com>,
        linux-kernel@...r.kernel.org
Cc:     rafael@...nel.org, lenb@...nel.org, linux-acpi@...r.kernel.org,
        linux-pm@...r.kernel.org, dave.hansen@...ux.intel.com,
        bp@...en8.de, tglx@...utronix.de, andi@...as.de, puwen@...on.cn,
        mario.limonciello@....com, peterz@...radead.org,
        rui.zhang@...el.com, gpiccoli@...lia.com,
        daniel.lezcano@...aro.org, ananth.narayan@....com,
        gautham.shenoy@....com, Calvin Ong <calvin.ong@....com>,
        stable@...r.kernel.org, regressions@...ts.linux.dev
Subject: Re: [PATCH] ACPI: processor_idle: Skip dummy wait for processors
 based on the Zen microarchitecture

On 9/20/22 23:36, K Prateek Nayak wrote:
> +	/*
> +	 * No delay is needed if we are in guest or on a processor
> +	 * based on the Zen microarchitecture.
> +	 */
> +	if (boot_cpu_has(X86_FEATURE_HYPERVISOR) || boot_cpu_has(X86_FEATURE_ZEN))
>  		return;

In the end, the delay is because of buggy, circa 2006 chipsets?  So, we
use a CPU vendor specific check to approximate that the chipset is
recent and not affected by the bug?  If so, is there no better way to
check for a newer chipset than this?

Do X86_FEATURE_ZEN CPUs just have unusually painful
inl(acpi_fadt.xpm_tmr_blk.address) implementations?  Is that why we
noticed all of a sudden?