Re: [PATCH] x86/domain: Drop the only-written smap_check_policy infrastructure

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

Hi,

On 08/05/18 17:20, Andrew Cooper wrote:
> On 08/05/18 17:10, Roger Pau Monné wrote:
>> On Tue, May 08, 2018 at 02:03:04PM +0100, Andrew Cooper wrote:
>>> c/s 4c5d78a10d "x86/pagewalk: Re-implement the pagetable walker" dropped the
>>> consumer of smap_policy.  Looking at c/s 31ae587e6f which introduced the
>>> smap_check logic, it exists only to work around a bug in guest_walk_tables()
>>> was resolved by the aformentioned commit.
>>>
>>> Remove the unused variables and associated infrastructure.
>>>
>>> Reported-by: Jason Andryuk <jandryuk@gmail.com>
>>> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
>> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
>>
>>> diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
>>> index 8b66096..197f8d6 100644
>>> --- a/xen/include/asm-x86/domain.h
>>> +++ b/xen/include/asm-x86/domain.h
>>> @@ -595,7 +583,6 @@ struct arch_vcpu
>>>   
>>>   struct guest_memory_policy
>>>   {
>>> -    smap_check_policy_t smap_policy;
>>>       bool nested_guest_mode;
>> Maybe guest_memory_policy could be dropped and
>> update_guest_memory_policy updated to take a bool nested_mode
>> parameter?
> 
> update_guest_memory_policy() stores the old value in the passed
> structure, and would more accurately be toggle_guest_memory_policy()
> when it came to guest mode.
> 
>> Or the function can be dropped altogether likely.
> 
> Sadly not yet.  This exists because of Xen's virtual-address based API
> for the shared info and time mappings.  This API is bad and wrong and
> wants fixing.  ISTR Juergen and Julien having plans to deal with this?

This should indeed be fixed properly, I was waiting some answer on my 
questions before attempting to go further on a fix (see [1] and [2]). I 
didn't have bandwidth so far to ping on the subject.

Cheers,

[1] 
https://www.mail-archive.com/xen-devel@lists.xenproject.org/msg08836.html
[2] 
https://www.mail-archive.com/xen-devel@lists.xenproject.org/msg08835.html

-- 
Julien Grall

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