linux-kernel - Re: [PATCH v2 04/43] arm64: RME: Handle Granule Protection Faults (GPFs)

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Date: Thu, 18 Apr 2024 14:17:14 +0100
From: Steven Price <steven.price@....com>
To: Suzuki K Poulose <suzuki.poulose@....com>, kvm@...r.kernel.org,
 kvmarm@...ts.linux.dev
Cc: Catalin Marinas <catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>,
 Will Deacon <will@...nel.org>, James Morse <james.morse@....com>,
 Oliver Upton <oliver.upton@...ux.dev>, Zenghui Yu <yuzenghui@...wei.com>,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Joey Gouly <joey.gouly@....com>, Alexandru Elisei
 <alexandru.elisei@....com>, Christoffer Dall <christoffer.dall@....com>,
 Fuad Tabba <tabba@...gle.com>, linux-coco@...ts.linux.dev,
 Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
Subject: Re: [PATCH v2 04/43] arm64: RME: Handle Granule Protection Faults
 (GPFs)

On 16/04/2024 12:17, Suzuki K Poulose wrote:
> On 12/04/2024 09:42, Steven Price wrote:
>> If the host attempts to access granules that have been delegated for use
>> in a realm these accesses will be caught and will trigger a Granule
>> Protection Fault (GPF).
>>
>> A fault during a page walk signals a bug in the kernel and is handled by
>> oopsing the kernel. A non-page walk fault could be caused by user space
>> having access to a page which has been delegated to the kernel and will
>> trigger a SIGBUS to allow debugging why user space is trying to access a
>> delegated page.
>>
>> Signed-off-by: Steven Price <steven.price@....com>
>> ---
>>   arch/arm64/mm/fault.c | 29 ++++++++++++++++++++++++-----
>>   1 file changed, 24 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
>> index 8251e2fea9c7..91da0f446dd9 100644
>> --- a/arch/arm64/mm/fault.c
>> +++ b/arch/arm64/mm/fault.c
>> @@ -765,6 +765,25 @@ static int do_tag_check_fault(unsigned long far,
>> unsigned long esr,
>>       return 0;
>>   }
>>   +static int do_gpf_ptw(unsigned long far, unsigned long esr, struct
>> pt_regs *regs)
>> +{
>> +    const struct fault_info *inf = esr_to_fault_info(esr);
>> +
>> +    die_kernel_fault(inf->name, far, esr, regs);
>> +    return 0;
>> +}
>> +
>> +static int do_gpf(unsigned long far, unsigned long esr, struct
>> pt_regs *regs)
>> +{
>> +    const struct fault_info *inf = esr_to_fault_info(esr);
>> +
>> +    if (!is_el1_instruction_abort(esr) && fixup_exception(regs))
>> +        return 0;
>> +
>> +    arm64_notify_die(inf->name, regs, inf->sig, inf->code, far, esr);
>> +    return 0;
>> +}
>> +
>>   static const struct fault_info fault_info[] = {
>>       { do_bad,        SIGKILL, SI_KERNEL,    "ttbr address size
>> fault"    },
>>       { do_bad,        SIGKILL, SI_KERNEL,    "level 1 address size
>> fault"    },
>> @@ -802,11 +821,11 @@ static const struct fault_info fault_info[] = {
>>       { do_alignment_fault,    SIGBUS,  BUS_ADRALN,    "alignment
>> fault"        },
>>       { do_bad,        SIGKILL, SI_KERNEL,    "unknown 34"            },
>>       { do_bad,        SIGKILL, SI_KERNEL,    "unknown 35"            },
> 
> Should this also be converted to do_gpf_ptw, "GPF at level -1", given we
> support LPA2 ?

Ah, yes I somehow missed that. Although something has gone majorly wrong
if this triggers! ;)

Steve

>> -    { do_bad,        SIGKILL, SI_KERNEL,    "unknown 36"            },
>> -    { do_bad,        SIGKILL, SI_KERNEL,    "unknown 37"            },
>> -    { do_bad,        SIGKILL, SI_KERNEL,    "unknown 38"            },
>> -    { do_bad,        SIGKILL, SI_KERNEL,    "unknown 39"            },
>> -    { do_bad,        SIGKILL, SI_KERNEL,    "unknown 40"            },
>> +    { do_gpf_ptw,        SIGKILL, SI_KERNEL,    "Granule Protection
>> Fault at level 0" },
>> +    { do_gpf_ptw,        SIGKILL, SI_KERNEL,    "Granule Protection
>> Fault at level 1" },
>> +    { do_gpf_ptw,        SIGKILL, SI_KERNEL,    "Granule Protection
>> Fault at level 2" },
>> +    { do_gpf_ptw,        SIGKILL, SI_KERNEL,    "Granule Protection
>> Fault at level 3" },
>> +    { do_gpf,        SIGBUS,  SI_KERNEL,    "Granule Protection Fault
>> not on table walk" },
>>       { do_bad,        SIGKILL, SI_KERNEL,    "level -1 address size
>> fault"    },
>>       { do_bad,        SIGKILL, SI_KERNEL,    "unknown 42"            },
>>       { do_translation_fault,    SIGSEGV, SEGV_MAPERR,    "level -1
>> translation fault"    },
> 
> 
> Rest looks fine to me.
> 
> Suzuki