linux-kernel - Re: [PATCH] xen/p2m: fix extra memory regions accounting

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Date:	Thu, 3 Sep 2015 14:25:42 +0200
From:	Juergen Gross <jgross@...e.com>
To:	Roger Pau Monne <roger.pau@...rix.com>,
	linux-kernel@...r.kernel.org
Cc:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	xen-devel@...ts.xenproject.org
Subject: Re: [PATCH] xen/p2m: fix extra memory regions accounting

On 09/03/2015 02:05 PM, Roger Pau Monne wrote:
> On systems with memory maps with ranges that don't end at page boundaries,
> like:
>
> [...]
> (XEN)  0000000000100000 - 00000000dfdf9c00 (usable)
> (XEN)  00000000dfdf9c00 - 00000000dfe4bc00 (ACPI NVS)
> [...]
>
> xen_add_extra_mem will create a protected range that ends up at 0xdfdf9c00,
> but the function used to check if a memory address is inside of a protected
> range works with pfns, which means that an attempt to map 0xdfdf9c00 will be
> refused because the check is performed against 0xdfdf9000 instead of
> 0xdfdf9c00.
>
> In order to fix this, make sure that the ranges that are added to the
> xen_extra_mem array are aligned to page boundaries.
>
> Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: David Vrabel <david.vrabel@...rix.com>
> Cc: Juergen Gross <jgross@...e.com>
> Cc: xen-devel@...ts.xenproject.org
> ---
> AFAICT this patch needs to be backported to 3.19, 4.0, 4.1 and 4.2.
> ---
>   arch/x86/xen/setup.c | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> index 55f388e..dcf5865 100644
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -68,6 +68,9 @@ static void __init xen_add_extra_mem(phys_addr_t start, phys_addr_t size)
>   {
>   	int i;
>
> +	start = PAGE_ALIGN(start);
> +	size &= PAGE_MASK;

This is not correct. If start wasn't page aligned and size was, you'll
add one additional page to xen_extra_mem.

> +
>   	for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++) {
>   		/* Add new region. */
>   		if (xen_extra_mem[i].size == 0) {
> @@ -92,6 +95,9 @@ static void __init xen_del_extra_mem(phys_addr_t start, phys_addr_t size)
>   	int i;
>   	phys_addr_t start_r, size_r;
>
> +	start = PAGE_ALIGN(start);
> +	size &= PAGE_MASK;

Not really needed, as xen_del_extra_mem() is called with aligned values
only. OTOH it does no harm, as long as you correct size as above.

> +
>   	for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++) {
>   		start_r = xen_extra_mem[i].start;
>   		size_r = xen_extra_mem[i].size;
>

Juergen
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