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Date:   Tue, 15 Nov 2022 12:48:34 -0800
From:   Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
To:     "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     Andrew Cooper <Andrew.Cooper3@citrix.com>, thomas.lendacky@amd.com,
        "H. Peter Anvin" <hpa@zytor.com>, hdegoede@redhat.com,
        Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, x86@kernel.org,
        Pavel Machek <pavel@ucw.cz>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        David.Kaplan@amd.com, Borislav Petkov <bp@alien8.de>,
        linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        Daniel Sneddon <daniel.sneddon@linux.intel.com>,
        antonio.gomez.iglesias@linux.intel.com
Subject: Re: [PATCH v3 2/2] x86/pm: Add enumeration check before spec MSRs
 save/restore setup
Message-ID: <20221115204834.dkb7yecr227lj277@desk>
References: <cover.1668539735.git.pawan.kumar.gupta@linux.intel.com>
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 <CAJZ5v0j6GBAx-UTTx2Oe1Y+bwpRuqifoNx4vBu1Vi9K93TS9JA@mail.gmail.com>
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On Tue, Nov 15, 2022 at 08:23:35PM +0100, Rafael J. Wysocki wrote:
>On Tue, Nov 15, 2022 at 8:17 PM Pawan Gupta
><pawan.kumar.gupta@linux.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@redhat.com>
>> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
>> Cc: stable@kernel.org
>
>Fine with me:
>
>Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Thanks.