Re: [RFC] powerpc/mm: Add validation for platform reserved memory ranges

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Anshuman Khandual <khandual@linux.vnet.ibm.com> writes:

> On 03/02/2016 05:40 PM, Michael Ellerman wrote:
>> On Wed, 2016-02-03 at 08:46:12 UTC, Anshuman Khandual wrote:
>>> For partition running on PHYP, there can be a adjunct partition
>>> which shares the virtual address range with the operating system.
>>> Virtual address ranges which can be used by the adjunct partition
>>> are communicated with virtual device node of the device tree with
>>> a property known as "ibm,reserved-virtual-addresses". This patch
>>> introduces a new function named 'validate_reserved_va_range' which
>>> is called inside 'setup_system' to validate that these reserved
>>> virtual address ranges do not overlap with the address ranges used
>>> by the kernel for all supported memory contexts. This helps prevent
>>> the possibility of getting return codes similar to H_RESOURCE for
>>> H_PROTECT hcalls for conflicting HPTE entries.
>> 
>> Good plan.
>
> Thanks !
>
>> 
>>> diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
>>> index 3d5abfe..95257c1 100644
>>> diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
>>> index 5c03a6a..04bc592 100644
>>> --- a/arch/powerpc/kernel/setup_64.c
>>> +++ b/arch/powerpc/kernel/setup_64.c
>>> @@ -546,6 +546,8 @@ void __init setup_system(void)
>>>  	smp_release_cpus();
>>>  #endif
>>>  
>>> +	validate_reserved_va_range();
>>> +
>> 
>> I don't see why this can't just be an initcall in hash_utils_64.c, rather than
>> being called from here.
>
> That works, will change it.
>
>> 
>>>  	pr_info("Starting Linux %s %s\n", init_utsname()->machine,
>>>  		 init_utsname()->version);
>>>  
>>> diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
>>> index ba59d59..03adafc 100644
>>> --- a/arch/powerpc/mm/hash_utils_64.c
>>> +++ b/arch/powerpc/mm/hash_utils_64.c
>>> @@ -810,6 +810,57 @@ void __init early_init_mmu(void)
>>>  	slb_initialize();
>>>  }
>>>  
>>> +/*
>>> + * PAPR says that each record contains 3 * 32 bit element, hence 12 bytes.
>>> + * First two element contains the abbreviated virtual address (high order
>>> + * 32 bits and low order 32 bits generates the abbreviated virtual address
>>> + * of 64 bits which need to be concatenated with 12 bits of 0 at the end
>>> + * to generate the actual 76 bit reserved virtual address) and size of the
>>> + * reserved virtual address range is encoded in next 32 bit element as number
>>> + * of 4K pages.
>>> + */
>>> +#define	BYTES_PER_RVA_RECORD	12
>> 
>> Please define a properly endian-annotated struct which encodes the layout.
>
> something like this ?
>
> struct reserved_va_record {
> 	__be32	high_addr;	/* High 32 bits of the abbreviated VA */
> 	__be32	low_addr;	/* Low 32 bits of the abbreviated VA */
> 	__be32	nr_4k;		/* VA range in multiple of 4K pages */
> };
>
>> 
>> It can be local to the function if that works.
>> 
>
> Okay.
>
>>> +/*
>>> + * Linux uses 65 bits (MAX_PHYSMEM_BITS + CONTEXT_BITS) from available 78
>>> + * bit wide virtual address range. As reserved virtual address range comes
>>> + * as an abbreviated form of 64 bits, we will use a partial address mask
>>> + * (65 bit mask >> 12) to match it for simplicity.
>>> + */
>>> +#define	PARTIAL_USED_VA_MASK	0x1FFFFFFFFFFFFFULL
>> 
>> Please calculate this from the appropriate constants. We don't want to have to
>> update it in future.
>
> Sure, I guess something like this works.
>
> #define RVA_SKIPPED_BITS        12      /* This changes with PAPR */
> #define USED_VA_BITS            MAX_PHYSMEM_BITS + CONTEXT_BITS

context + esid + sid shift it should be


> #define PARTIAL_USED_VA_MASK    ((1ULL << (USED_VA_BITS - RVA_SKIPPED_BITS)) - 1)
>
>> 
>>> +void __init validate_reserved_va_range(void)
>>> +{
>>> +	struct device_node *np;
>>> +	struct property *prop;
>>> +	unsigned int size, count, i;
>>> +	const __be32 *value;
>>> +	__be64 vaddr;
>>> +
>>> +	np = of_find_node_by_name(NULL, "vdevice");
>>> +	if (!np)
>>> +		return;
>>> +
>>> +	prop = of_find_property(np, "ibm,reserved-virtual-addresses", NULL);
>>> +	if (!prop)
>>> +		return;
>> 
>> You don't need to do a find, the get below will do it for you.
>
> Sure.
>
>> 
>>> +	value = of_get_property(np, "ibm,reserved-virtual-addresses", &size);
>>> +	if (!value)
>>> +		return;
>>> +
>>> +	count = size / BYTES_PER_RVA_RECORD;
>>> +	for (i = 0; i < count; i++) {
>>> +		vaddr = ((__be64) value[i * 3] << 32) | value[i * 3 + 1];
>>> +		if (vaddr & ~PARTIAL_USED_VA_MASK) {
>> 
>> How can it work to test a __be64 against a non-byte-swapped mask ? But like I
>> said above, please do this with a struct and proper endian conversions.
>
> sure.
>
>> 
>>> +			pr_info("Reserved virtual address range starting "
>>> +				"at [%llx000] verified for overlap\n", vaddr);
>> 
>> This should print nothing in the success case.
>
> Not even as a pr_devel level message ? 
>
>> 
>>> +			continue;
>>> +		}
>>> +		BUG_ON("Reserved virtual address range overlapping");
>> 
>> But here you should provide more detail. The first thing a debugger will need
>> to know is what address overlapped.
>
> Sure, will provide the starting VA and the size of the range.

-aneesh