Re: [PATCH v3 7/8] xen/arm: Rework the interface of p2m_lookup and use typesafe gfn and mfn

[Julien Grall <julien.grall@arm.com>]

Hi Stefano,

On 23/06/16 15:14, Stefano Stabellini wrote:
> On Tue, 21 Jun 2016, Julien Grall wrote:
>> The prototype and the declaration of p2m_lookup disagree on how the
>> function should be used. One expect a frame number whilst the other
>> an address.
>>
>> Thankfully, everyone is using with an address today. However, most of
>> the callers have to convert a guest frame to an address. Modify
>> the interface to take a guest physical frame in parameter and return
>> a machine frame.
>>
>> Whilst modifying the interface, use typesafe gfn and mfn for clarity
>> and catching possible misusage.
>>
>> Signed-off-by: Julien Grall <julien.grall@arm.com>
>> ---
>>   xen/arch/arm/p2m.c        | 37 ++++++++++++++++++++-----------------
>>   xen/arch/arm/traps.c      | 21 +++++++++++----------
>>   xen/include/asm-arm/p2m.h |  7 +++----
>>   3 files changed, 34 insertions(+), 31 deletions(-)
>>
>> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
>> index 47cb383..f3330dd 100644
>> --- a/xen/arch/arm/p2m.c
>> +++ b/xen/arch/arm/p2m.c
>> @@ -140,14 +140,15 @@ void flush_tlb_domain(struct domain *d)
>>   }
>>
>>   /*
>> - * Lookup the MFN corresponding to a domain's PFN.
>> + * Lookup the MFN corresponding to a domain's GFN.
>>    *
>>    * There are no processor functions to do a stage 2 only lookup therefore we
>>    * do a a software walk.
>>    */
>> -static paddr_t __p2m_lookup(struct domain *d, paddr_t paddr, p2m_type_t *t)
>> +static mfn_t __p2m_lookup(struct domain *d, gfn_t gfn, p2m_type_t *t)
>>   {
>>       struct p2m_domain *p2m = &d->arch.p2m;
>> +    const paddr_t paddr = pfn_to_paddr(gfn_x(gfn));
>>       const unsigned int offsets[4] = {
>>           zeroeth_table_offset(paddr),
>>           first_table_offset(paddr),
>> @@ -158,7 +159,7 @@ static paddr_t __p2m_lookup(struct domain *d, paddr_t paddr, p2m_type_t *t)
>>           ZEROETH_MASK, FIRST_MASK, SECOND_MASK, THIRD_MASK
>>       };
>>       lpae_t pte, *map;
>> -    paddr_t maddr = INVALID_PADDR;
>> +    mfn_t mfn = _mfn(INVALID_MFN);
>
> It might be worth defining INVALID_MFN_T and just assign that to mfn.

Good idea. It will be useful in other places too.

>
>>       paddr_t mask = 0;
>>       p2m_type_t _t;
>>       unsigned int level, root_table;


[...]

>> @@ -1561,11 +1565,10 @@ p2m_mem_access_check_and_get_page(vaddr_t gva, unsigned long flag)
>>        * We had a mem_access permission limiting the access, but the page type
>>        * could also be limiting, so we need to check that as well.
>>        */
>> -    maddr = __p2m_lookup(current->domain, ipa, &t);
>> -    if ( maddr == INVALID_PADDR )
>> +    mfn = mfn_x(__p2m_lookup(current->domain, gfn, &t));
>> +    if ( mfn == INVALID_MFN )
>
> The conversion would go away if we had an INVALID_MFN which is mfn_t

Will do.

Regards,

-- 
Julien Grall

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