[MODERATED] Re: [PATCH 1/2] L1TF KVM 1

[Dave Hansen <dave.hansen@linux.intel.com>]

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On 05/29/2018 12:42 PM, speck for Paolo Bonzini wrote:
>  	r = -ENOMEM;
> +	page = alloc_pages(GFP_ATOMIC, L1D_CACHE_ORDER);
> +	if (!page)
> +		goto out;
> +	empty_zero_pages = page_address(page);

There is also an Intel suggestion to have guard pages before and after
the L1D flush buffer.  As it stands, the prefetchers might pull data
into the cache from pages adjacent to the allocation you have there.

You can use vmalloc(), where we get (unmapped) guard pages already.  Or,
you can just oversize the allocation using:

	alloc_pages_exact(L1D_CACHE_ORDER * PAGE_SIZE + 2 * PAGE_SIZE)

and just point empty_zero_pages to the second page in the buffer:

	empty_zero_pages = page_address(page + 1);

I'd suggest the alloc_pages_exact() version.  It will chew up fewer TLB
entries.