Re: [PATCH] x86/sgx: Remove unnecessary kmap() from sgx_ioc_enclave_init()

[Jarkko Sakkinen]

On Wed, Mar 24, 2021 at 11:22:46AM -0700, ira.weiny@xxxxxxxxx wrote:
> From: Ira Weiny <ira.weiny@xxxxxxxxx>
> 
> kmap is inefficient and is being replaced by kmap_local_page(), if
> possible.

Nit: just saying that something is inefficient is not enough. Always
should have something to back it up.

> That said, there is no readily apparent reason why initp_page needs to
> be allocated and kmap'ed() except that 'sigstruct' needs to be page
> aligned and 'token' 512 byte aligned.
> 
> Rather than change this kmap() to kmap_local_page() use kmalloc()
> instead because kmalloc() can gives this alignment when allocating
> PAGE_SIZE bytes.
> 
> Remove the alloc_page()/kmap() and replace with kmalloc(PAGE_SIZE, ...)
> to get a page aligned kernel address.
> 
> In addition add a comment to document the alignment requirements so that
> others don't attempt to 'fix' this again.

I'm a bit confused based on this commit message. Why is kmap_local_page()
better, and why kmalloc() is the ultimate choice of all three options?

> 
> Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
> Cc: Jethro Beekman <jethro@xxxxxxxxxxxx>
> Cc: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
 
/Jarkko