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Date:   Sun, 4 Oct 2020 23:27:50 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc:     x86@kernel.org, linux-sgx@vger.kernel.org,
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Subject: Re: [PATCH v39 11/24] x86/sgx: Add SGX enclave driver
Message-ID: <20201004222750.GI20115@casper.infradead.org>
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 <20201003195440.GD20115@casper.infradead.org>
 <20201004215049.GA43926@linux.intel.com>
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Precedence: bulk

On Mon, Oct 05, 2020 at 12:50:49AM +0300, Jarkko Sakkinen wrote:
> What is shoukd take is encl->lock.
> 
> The loop was pre-v36 like:
> 
> 	idx_start = PFN_DOWN(start);
> 	idx_end = PFN_DOWN(end - 1);
> 
> 	for (idx = idx_start; idx <= idx_end; ++idx) {
> 		mutex_lock(&encl->lock);
> 		page = radix_tree_lookup(&encl->page_tree, idx);
> 		mutex_unlock(&encl->lock);
> 
> 		if (!page || (~page->vm_max_prot_bits & vm_prot_bits))
> 			return -EACCES;
> 	}
> 
> Looking at xarray.h and filemap.c, I'm thinking something along the
> lines of:
> 
> 	for (idx = idx_start; idx <= idx_end; ++idx) {
> 		mutex_lock(&encl->lock);
> 		page = xas_find(&xas, idx + 1);
> 		mutex_unlock(&encl->lock);
> 
> 		if (!page || (~page->vm_max_prot_bits & vm_prot_bits))
> 			return -EACCES;
> 	}
> 
> Does this look about right?

Not really ...

	int ret = 0;

	mutex_lock(&encl->lock);
	rcu_read_lock();
	while (xas.index < idx_end) {
		page = xas_next(&xas);
		if (!page || (~page->vm_max_prot_bits & vm_prot_bits))
			ret = -EACCESS;
			break;
		}
	}
	rcu_read_unlock();
	mutex_unlock(&encl->lock);

	return ret;

... or you could rework to use the xa_lock instead of encl->lock.
I don't know how feasible that is for you.