Re: [PATCH 1/2] x86_64,entry: Filter RFLAGS.NT on entry from userspace

[H. Peter Anvin]

On 09/30/2014 04:21 PM, Thomas Gleixner wrote:
>>
>> If we ever want those cycles back, I bet that the compat sysenter path
>> could be trimmed down a lot.  For example, I think that all of the
>> zero-extension stuff is unnecessary now that we have the magic syscall
>> wrappers for all (?) syscalls.
> 
> Emphasis on "(?)". So yes, once we verified that ....
> 

I don't think that's true.  Many system calls use exactly the same entry
point for compat and noncompat calls.  I don't see any value in
replicating that code in every system call.

The only time we need to do anything horribly special is when we have an
argument which is a signed long, which fortunately is not at all common.

	-hpa


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