Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 26 Mar 2021 21:45:24 +0200
From:   Jarkko Sakkinen <jarkko@kernel.org>
To:     ira.weiny@intel.com
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, Sean Christopherson <seanjc@google.com>,
        Jethro Beekman <jethro@fortanix.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        linux-sgx@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/sgx: Remove unnecessary kmap() from
 sgx_ioc_enclave_init()
Message-ID: <YF451PGNd8x/i56z@kernel.org>
References: <20210324182246.2484875-1-ira.weiny@intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20210324182246.2484875-1-ira.weiny@intel.com>
Precedence: bulk

On Wed, Mar 24, 2021 at 11:22:46AM -0700, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
> 
> 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@google.com>
> Cc: Jethro Beekman <jethro@fortanix.com>
> Cc: Jarkko Sakkinen <jarkko@kernel.org>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
 
/Jarkko