linux-kernel - Re: [PATCH v3 2/2] x86/pm: Add enumeration check before spec MSRs save/restore setup

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Date:   Tue, 15 Nov 2022 20:23:35 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc:     Andrew Cooper <Andrew.Cooper3@...rix.com>, thomas.lendacky@....com,
        "H. Peter Anvin" <hpa@...or.com>, hdegoede@...hat.com,
        Ingo Molnar <mingo@...hat.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        Pavel Machek <pavel@....cz>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David.Kaplan@....com, Borislav Petkov <bp@...en8.de>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        antonio.gomez.iglesias@...ux.intel.com
Subject: Re: [PATCH v3 2/2] x86/pm: Add enumeration check before spec MSRs
 save/restore setup

On Tue, Nov 15, 2022 at 8:17 PM Pawan Gupta
<pawan.kumar.gupta@...ux.intel.com> wrote:
>
> pm_save_spec_msr() keeps a list of all the MSRs which _might_ need to be
> saved and restored at hibernate and resume.  However, it has zero
> awareness of CPU support for these MSRs.  It mostly works by
> unconditionally attempting to manipulate these MSRs and relying on
> rdmsrl_safe() being able to handle a #GP on CPUs where the support is
> unavailable.
>
> However, it's possible for reads (RDMSR) to be supported for a given MSR
> while writes (WRMSR) are not.  In this case, msr_build_context() sees a
> successful read (RDMSR) and marks the MSR as 'valid'.  Then, later, a
> write (WRMSR) fails, producing a nasty (but harmless) error message.
> This causes restore_processor_state() to try and restore it, but writing
> this MSR is not allowed on the Intel Atom N2600 leading to:
>
>   unchecked MSR access error: WRMSR to 0x122 (tried to write 0x0000000000000002) \
>      at rIP: 0xffffffff8b07a574 (native_write_msr+0x4/0x20)
>   Call Trace:
>    <TASK>
>    restore_processor_state
>    x86_acpi_suspend_lowlevel
>    acpi_suspend_enter
>    suspend_devices_and_enter
>    pm_suspend.cold
>    state_store
>    kernfs_fop_write_iter
>    vfs_write
>    ksys_write
>    do_syscall_64
>    ? do_syscall_64
>    ? up_read
>    ? lock_is_held_type
>    ? asm_exc_page_fault
>    ? lockdep_hardirqs_on
>    entry_SYSCALL_64_after_hwframe
>
> To fix this, add the corresponding X86_FEATURE bit for each MSR.  Avoid
> trying to manipulate the MSR when the feature bit is clear. This
> required adding a X86_FEATURE bit for MSRs that do not have one already,
> but it's a small price to pay.
>
> Fixes: 73924ec4d560 ("x86/pm: Save the MSR validity status at context setup")
> Reported-by: Hans de Goede <hdegoede@...hat.com>
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> Cc: stable@...nel.org

Fine with me:

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

> ---
>  arch/x86/power/cpu.c | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
> index 4cd39f304e20..11a7e28f8985 100644
> --- a/arch/x86/power/cpu.c
> +++ b/arch/x86/power/cpu.c
> @@ -511,18 +511,27 @@ static int pm_cpu_check(const struct x86_cpu_id *c)
>         return ret;
>  }
>
> +struct msr_enumeration {
> +       u32 msr_no;
> +       u32 feature;
> +};
> +
>  static void pm_save_spec_msr(void)
>  {
> -       u32 spec_msr_id[] = {
> -               MSR_IA32_SPEC_CTRL,
> -               MSR_IA32_TSX_CTRL,
> -               MSR_TSX_FORCE_ABORT,
> -               MSR_IA32_MCU_OPT_CTRL,
> -               MSR_AMD64_LS_CFG,
> -               MSR_AMD64_DE_CFG,
> +       struct msr_enumeration msr_enum[] = {
> +               {MSR_IA32_SPEC_CTRL,    X86_FEATURE_MSR_SPEC_CTRL},
> +               {MSR_IA32_TSX_CTRL,     X86_FEATURE_MSR_TSX_CTRL},
> +               {MSR_TSX_FORCE_ABORT,   X86_FEATURE_TSX_FORCE_ABORT},
> +               {MSR_IA32_MCU_OPT_CTRL, X86_FEATURE_SRBDS_CTRL},
> +               {MSR_AMD64_LS_CFG,      X86_FEATURE_LS_CFG_SSBD},
> +               {MSR_AMD64_DE_CFG,      X86_FEATURE_LFENCE_RDTSC},
>         };
> +       int i;
>
> -       msr_build_context(spec_msr_id, ARRAY_SIZE(spec_msr_id));
> +       for (i = 0; i < ARRAY_SIZE(msr_enum); i++) {
> +               if (boot_cpu_has(msr_enum[i].feature))
> +                       msr_build_context(&msr_enum[i].msr_no, 1);
> +       }
>  }
>
>  static int pm_check_save_msr(void)
> --
> 2.37.3
>