linux-kernel - Re: [RFC PATCH v2 29/35] irqchip/gic-v3: Don't return errors from gic_acpi_match

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Message-ID: <0743752e-fd7a-c0b6-a193-196aef12b2a3@redhat.com>
Date:   Tue, 19 Sep 2023 13:51:37 +1000
From:   Gavin Shan <gshan@...hat.com>
To:     James Morse <james.morse@....com>, linux-pm@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-acpi@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, kvmarm@...ts.linux.dev
Cc:     x86@...nel.org, Salil Mehta <salil.mehta@...wei.com>,
        Russell King <linux@...linux.org.uk>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        jianyong.wu@....com, justin.he@....com
Subject: Re: [RFC PATCH v2 29/35] irqchip/gic-v3: Don't return errors from
 gic_acpi_match_gicc()

On 9/19/23 13:39, Gavin Shan wrote:
> 
> On 9/14/23 02:38, James Morse wrote:
>> gic_acpi_match_gicc() is only called via gic_acpi_count_gicr_regions().
>> It should only count the number of enabled redistributors, but it
>> also tries to sanity check the GICC entry, currently returning an
>> error if the Enabled bit is set, but the gicr_base_address is zero.
>>
>> Adding support for the online-capable bit to the sanity check
>> complicates it, for no benefit. The existing check implicitly
>> depends on gic_acpi_count_gicr_regions() previous failing to find
>> any GICR regions (as it is valid to have gicr_base_address of zero if
>> the redistributors are described via a GICR entry).
>>
>> Instead of complicating the check, remove it. Failures that happen
>> at this point cause the irqchip not to register, meaning no irqs
>> can be requested. The kernel grinds to a panic() pretty quickly.
>>
>> Without the check, MADT tables that exhibit this problem are still
>> caught by gic_populate_rdist(), which helpfully also prints what
>> went wrong:
>> | CPU4: mpidr 100 has no re-distributor!
>>
>> Signed-off-by: James Morse <james.morse@....com>
>> ---
>>   drivers/irqchip/irq-gic-v3.c | 18 ++++++------------
>>   1 file changed, 6 insertions(+), 12 deletions(-)
>>
> 
> With below nits resolved:
> 
> Reviewed-by: Gavin Shan <gshan@...hat.com>
> 
>> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
>> index 72d3cdebdad1..0f54811262eb 100644
>> --- a/drivers/irqchip/irq-gic-v3.c
>> +++ b/drivers/irqchip/irq-gic-v3.c
>> @@ -2415,21 +2415,15 @@ static int __init gic_acpi_match_gicc(union acpi_subtable_headers *header,
>>       /*
>>        * If GICC is enabled and has valid gicr base address, then it means
>> -     * GICR base is presented via GICC
>> +     * GICR base is presented via GICC. The redistributor is only known to
>> +     * be accessible if the GICC is marked as enabled. If this bit is not
>> +     * set, we'd need to add the redistributor at runtime, which isn't
>> +     * supported.
>>        */
>> -    if (acpi_gicc_is_usable(gicc) && gicc->gicr_base_address) {
>> +    if (gicc->flags & ACPI_MADT_ENABLED && gicc->gicr_base_address)
>>           acpi_data.enabled_rdists++;
>> -        return 0;
>> -    }
> 
>      if (acpi_gicc_is_usable(gicc) && gicc->gicr_base_address) {
> 

Please ignore this since acpi_gicc_is_usable() is changed to cover
the bit ACPI_MADT_GICC_CPU_CAPABLE in next patch, which means
"(gicc->flags & ACPI_MADT_ENABLED)" is needed here.

> 
>> -    /*
>> -     * It's perfectly valid firmware can pass disabled GICC entry, driver
>> -     * should not treat as errors, skip the entry instead of probe fail.
>> -     */
>> -    if (!acpi_gicc_is_usable(gicc))
>> -        return 0;
>> -
>> -    return -ENODEV;
>> +    return 0;
>>   }
>>   static int __init gic_acpi_count_gicr_regions(void)

Thanks,
Gavin