Re: [PATCH v5 04/43] arm64: RME: Handle Granule Protection Faults (GPFs)

[Steven Price <steven.price@arm.com>]

On 24/10/2024 15:17, Aneesh Kumar K.V wrote:
> Steven Price <steven.price@arm.com> writes:
> 
>> 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.
>>
> 
> A non-page walk fault can also be caused by host kernel trying to access a
> page which it had delegated before. It would be nice to dump details
> like FAR in that case. Right now it shows only the below.

While I agree FAR would be handy, this isn't specific to a GPF.

arm64_notify_die() takes the FAR, but in the case of a kernel fault
ignores it and calls die(). I'm not sure if there's a good reason for it
not calling die_kernel_fault() instead which would print the FAR. Or
indeed whether the FAR should be passed instead of the ESR (although
changing that now would probably be confusing).

This affects e.g. do_sea(), do_mem_abort() and others too. It might be
worth sending a patch to improve that behaviour, but I think the
handling for GPFs of using arm64_notify_die() is correct.

Thanks,
Steve

> [  285.122310] Internal error: Granule Protection Fault not on table walk: 0000000096000068 [#1] PREEMPT SMP               
> [  285.122427] Modules linked in:                                                                                                                                                
> [  285.122512] CPU: 1 UID: 0 PID: 217 Comm: kvm-vcpu-0 Not tainted 6.12.0-rc1-00082-g8461d8333829 #42
> [  285.122656] Hardware name: FVP Base RevC (DT)
> [  285.122733] pstate: 81400009 (Nzcv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
> [  285.122871] pc : clear_page+0x18/0x50
> [  285.122975] lr : kvm_gmem_get_pfn+0xbc/0x190
> [  285.123110] sp : ffff800082cef900
> [  285.123182] x29: ffff800082cef910 x28: 0000000090000000 x27: 0000000090000006
> .....
> 
> -aneesh
> 
>>
>> Signed-off-by: Steven Price <steven.price@arm.com>
>> ---
>> Changes since v2:
>>  * Include missing "Granule Protection Fault at level -1"
>> ---
>>  arch/arm64/mm/fault.c | 31 +++++++++++++++++++++++++------
>>  1 file changed, 25 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
>> index 8b281cf308b3..f9d72a936d48 100644
>> --- a/arch/arm64/mm/fault.c
>> +++ b/arch/arm64/mm/fault.c
>> @@ -804,6 +804,25 @@ 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"	},
>> @@ -840,12 +859,12 @@ static const struct fault_info fault_info[] = {
>>  	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 32"			},
>>  	{ do_alignment_fault,	SIGBUS,  BUS_ADRALN,	"alignment fault"		},
>>  	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 34"			},
>> -	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 35"			},
>> -	{ 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 -1" },
>> +	{ 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"	},
>> -- 
>> 2.34.1