linux-kernel - Re: [PATCH] x86: Remove unnecessary kmap() from sgx_ioc_enclave

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Message-ID: <20210201084812.GA3229269@infradead.org>
Date:   Mon, 1 Feb 2021 08:48:12 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     ira.weiny@...el.com, Jarkko Sakkinen <jarkko@...nel.org>,
        linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org
Subject: Re: [PATCH] x86: Remove unnecessary kmap() from
 sgx_ioc_enclave_init()

On Fri, Jan 29, 2021 at 09:37:30AM -0800, Sean Christopherson wrote:
> On Thu, Jan 28, 2021, ira.weiny@...el.com wrote:
> > From: Ira Weiny <ira.weiny@...el.com>
> > 
> > There is no reason to alloc a page and kmap it to store this temporary
> > data from the user. 
> 
> Actually, there is, it's just poorly documented.  The sigstruct needs to be
> page aligned, and the token needs to be 512-byte aligned.  kmcalloc doesn't
> guarantee alignment.  IIRC things will work until slub_debug is enabled, at
> which point the natural alignment behavior goes out the window.

Well, there still is absolutely no need for the kmap as you can use
page_address for a GFP_KERNEL allocation.