Re: [Xen-devel] [PATCH 16/17] xen/mm: Convert {s, g}et_gpfn_from_mfn() to use typesafe MFN

[Julien Grall <julien@xen.org>]

Hi,

On 23/03/2020 12:11, Hongyan Xia wrote:
> On Sun, 2020-03-22 at 16:14 +0000, julien@xen.org wrote:
>> From: Julien Grall <julien.grall@arm.com>
>>
>> The first parameter of {s,g}et_gpfn_from_mfn() is an MFN, so it can
>> be
>> switched to use the typesafe.
>>
>> At the same time, replace gpfn with pfn in the helpers as they all
>> deal
>> with PFN and also turn the macros to static inline.
>>
>> Note that the return of the getter and the 2nd parameter of the
>> setter
>> have not been converted to use typesafe PFN because it was requiring
>> more changes than expected.
>>
>> Signed-off-by: Julien Grall <julien.grall@arm.com>
>>
>> ---
>>      This was originally sent as part of "xen/arm: Properly disable
>> M2P
>>      on Arm" [1].
>>
>>      Changes since the original version:
>>          - mfn_to_gmfn() is still present for now so update it
>>          - Remove stray +
>>          - Avoid churn in set_pfn_from_mfn() by inverting mfn and mfn_
>>          - Remove tags
>>          - Fix build in mem_sharing
>>
>>      [1] <20190603160350.29806-1-julien.grall@arm.com>
>> ---
>>   xen/arch/x86/cpu/mcheck/mcaction.c |  2 +-
>>   xen/arch/x86/mm.c                  | 14 +++----
>>   xen/arch/x86/mm/mem_sharing.c      | 20 ++++-----
>>   xen/arch/x86/mm/p2m-pod.c          |  4 +-
>>   xen/arch/x86/mm/p2m-pt.c           | 35 ++++++++--------
>>   xen/arch/x86/mm/p2m.c              | 66 +++++++++++++++-------------
>> --
>>   xen/arch/x86/mm/paging.c           |  4 +-
>>   xen/arch/x86/pv/dom0_build.c       |  6 +--
>>   xen/arch/x86/x86_64/traps.c        |  8 ++--
>>   xen/common/page_alloc.c            |  2 +-
>>   xen/include/asm-arm/mm.h           |  2 +-
>>   xen/include/asm-x86/grant_table.h  |  2 +-
>>   xen/include/asm-x86/mm.h           | 12 ++++--
>>   xen/include/asm-x86/p2m.h          |  2 +-
>>   14 files changed, 93 insertions(+), 86 deletions(-)
>>
>>
> 
> [...]
> 
>> diff --git a/xen/include/asm-arm/mm.h b/xen/include/asm-arm/mm.h
>> index abf4cc23e4..11614f9107 100644
>> --- a/xen/include/asm-arm/mm.h
>> +++ b/xen/include/asm-arm/mm.h
>> @@ -319,7 +319,7 @@ struct page_info *get_page_from_gva(struct vcpu
>> *v, vaddr_t va,
>>   #define SHARED_M2P(_e)           ((_e) == SHARED_M2P_ENTRY)
>>   
>>   /* Xen always owns P2M on ARM */
>> -#define set_gpfn_from_mfn(mfn, pfn) do { (void) (mfn), (void)(pfn);
>> } while (0)
>> +static inline void set_pfn_from_mfn(mfn_t mfn, unsigned long pfn) {}
>>   #define mfn_to_gmfn(_d, mfn)  (mfn)
> 
> I do not have a setup to compile and test code for Arm, but wouldn't
> the compiler complain about unused arguments here? The marco version
> explicitly silenced compiler complaints.

The macro version does not use (void)(arg) for silencing unused 
parameter. It is for evaluating (mfn) but ignore the result. A compiler 
would warn without (void) because we build Xen with -Wall which include 
-Wunused-value.

Xen is not used with -Wunused-parameter, so there is no concern about 
unused parameters. If we ever decided to turn on -Wunused-parameter (or 
-Wextra), then we will have quite a bit of code to modify (such as 
callbacks not using all the parameters) to make it compile.

>   
>> diff --git a/xen/include/asm-x86/grant_table.h b/xen/include/asm-
>> x86/grant_table.h
>> index 5871238f6d..b6a09c4c6c 100644
>> --- a/xen/include/asm-x86/grant_table.h
>> +++ b/xen/include/asm-x86/grant_table.h
>> @@ -41,7 +41,7 @@ static inline int
>> replace_grant_host_mapping(uint64_t addr, mfn_t frame,
>>   #define gnttab_get_frame_gfn(gt, st, idx)
>> ({                             \
>>       mfn_t mfn_ = (st) ? gnttab_status_mfn(gt,
>> idx)                       \
>>                         : gnttab_shared_mfn(gt,
>> idx);                      \
>> -    unsigned long gpfn_ =
>> get_gpfn_from_mfn(mfn_x(mfn_));                \
>> +    unsigned long gpfn_ =
>> get_pfn_from_mfn(mfn_);                        \
>>       VALID_M2P(gpfn_) ? _gfn(gpfn_) :
>> INVALID_GFN;                        \
>>   })
>>   
>> diff --git a/xen/include/asm-x86/mm.h b/xen/include/asm-x86/mm.h
>> index 53f2ed7c7d..2a4f42e78f 100644
>> --- a/xen/include/asm-x86/mm.h
>> +++ b/xen/include/asm-x86/mm.h
>> @@ -500,9 +500,10 @@ extern paddr_t mem_hotplug;
>>    */
>>   extern bool machine_to_phys_mapping_valid;
>>   
>> -static inline void set_gpfn_from_mfn(unsigned long mfn, unsigned
>> long pfn)
>> +static inline void set_pfn_from_mfn(mfn_t mfn_, unsigned long pfn)
>>   {
>> -    const struct domain *d = page_get_owner(mfn_to_page(_mfn(mfn)));
>> +    const unsigned long mfn = mfn_x(mfn_);
>> +    const struct domain *d = page_get_owner(mfn_to_page(mfn_));
>>       unsigned long entry = (d && (d == dom_cow)) ? SHARED_M2P_ENTRY :
>> pfn;
>>   
>>       if ( !machine_to_phys_mapping_valid )
>> @@ -515,11 +516,14 @@ static inline void set_gpfn_from_mfn(unsigned
>> long mfn, unsigned long pfn)
>>   
>>   extern struct rangeset *mmio_ro_ranges;
>>   
>> -#define get_gpfn_from_mfn(mfn)      (machine_to_phys_mapping[(mfn)])
>> +static inline unsigned long get_pfn_from_mfn(mfn_t mfn)
>> +{
>> +    return machine_to_phys_mapping[mfn_x(mfn)];
>> +}
> 
> Any specific reason this (and some other macros) are turned into static
> inline? I don't have a problem with them being inline functions but
> just wondering if there is a reason to do so.

static inline provides better safety check than macro. So we tend to 
switch to static inline whenever the headers inter-dependency madness is 
not interplaying.

>   
>>   #define mfn_to_gmfn(_d, mfn)                            \
>>       ( (paging_mode_translate(_d))                       \
>> -      ? get_gpfn_from_mfn(mfn)                          \
>> +      ? get_pfn_from_mfn(_mfn(mfn))                     \
>>         : (mfn) )
>>   
>>   #define compat_pfn_to_cr3(pfn) (((unsigned)(pfn) << 12) |
>> ((unsigned)(pfn) >> 20))
>> diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
>> index a2c6049834..39dae242b0 100644
>> --- a/xen/include/asm-x86/p2m.h
>> +++ b/xen/include/asm-x86/p2m.h
>> @@ -505,7 +505,7 @@ static inline struct page_info
>> *get_page_from_gfn(
>>   static inline gfn_t mfn_to_gfn(const struct domain *d, mfn_t mfn)
>>   {
>>       if ( paging_mode_translate(d) )
>> -        return _gfn(get_gpfn_from_mfn(mfn_x(mfn)));
>> +        return _gfn(get_pfn_from_mfn(mfn));
>>       else
>>           return _gfn(mfn_x(mfn));
>>   }
> 
> Apart from the two comments above, looks good to me.
> 
> Reviewed-by: Hongyan Xia <hongyxia@amazon.com>

Thank you!

Cheers,

-- 
Julien Grall

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