Re: [Xen-devel] [PATCH] x86/xen: do not identity map E820 memory regions that are UNUSABLE

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On 09/07/13 14:38, David Vrabel wrote:
> From: David Vrabel <david.vrabel@xxxxxxxxxx>
>
> If there are UNUSABLE regions in the machine memory map, dom0 will
> attempt to map them 1:1 which is not permitted by Xen and the kernel
> will crash.
>
> There isn't anything interesting in the UNUSABLE region that the dom0
> kernel needs access to so we can avoid making the 1:1 mapping and
> leave the region as RAM.
>
> Since the obtaining the memory map for dom0 and domU are now more
> different, refactor each into separate functions.
>
> This fixes a dom0 boot failure if tboot is used (because tboot was
> marking a memory region as UNUSABLE).
>
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx

I tested it with Xen 4.1.3-rc and Linux 3.8.13.4 and it is fixing the
early boot crash I reported.

Tested-by: Aurelien Chartier <aurelien.chartier@xxxxxxxxxx>

> ---
>  arch/x86/xen/setup.c |  114 ++++++++++++++++++++++++++++++++++++++++----------
>  1 files changed, 91 insertions(+), 23 deletions(-)
>
> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> index 94eac5c..3fdb6bd 100644
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -55,6 +55,91 @@ unsigned long xen_released_pages;
>   */
>  #define EXTRA_MEM_RATIO		(10)
>  
> +static int __init xen_get_memory_map_dom0(struct e820entry *map,
> +					  unsigned *nr_entries)
> +{
> +	struct xen_memory_map memmap;
> +	unsigned i;
> +	int ret;
> +
> +	/*
> +	 * Dom0 requires access to machine addresses for BIOS data and
> +	 * MMIO (e.g. PCI) devices.  The reset of the kernel expects
> +	 * to be able to access these through a 1:1 p2m mapping.
> +	 *
> +	 * We need to take the pseudo physical memory map and set up
> +	 * 1:1 mappings corresponding to the RESERVED regions and
> +	 * holes in the /machine/ memory map, adding/expanding the RAM
> +	 * region at the end of the map for the relocated RAM.
> +	 *
> +	 * This is more easily done if we just start with the machine
> +	 * memory map.
> +	 *
> +	 * UNUSABLE regions are awkward, they are not interesting to
> +	 * dom0 and Xen won't allow them to be mapped so we want to
> +	 * leave these as RAM in the pseudo physical map.
> +	 *
> +	 * Again, this is easiest if we take the machine memory map
> +	 * and change the UNUSABLE regions to RAM.
> +	 */
> +
> +	memmap.nr_entries = *nr_entries;
> +	set_xen_guest_handle(memmap.buffer, map);
> +
> +	ret = HYPERVISOR_memory_op(XENMEM_machine_memory_map, &memmap);
> +	if (ret < 0)
> +		return ret;
> +
> +	for (i = 0; i < memmap.nr_entries; i++) {
> +		if (map[i].type == E820_UNUSABLE)
> +			map[i].type = E820_RAM;
> +	}
> +
> +	*nr_entries = memmap.nr_entries;
> +	return 0;
> +}
> +
> +static int __init xen_get_memory_map_domu(struct e820entry *map,
> +					  unsigned *nr_entries)
> +{
> +	struct xen_memory_map memmap;
> +	int ret;
> +
> +	/*
> +	 * For domUs, use the psuedo-physical memory map.

Small typo here.

> +	 *
> +	 * If this is not available, fake up a memory map with a
> +	 * single region containing the initial number of pages.
> +	 */
> +
> +	memmap.nr_entries = *nr_entries;
> +	set_xen_guest_handle(memmap.buffer, map);
> +
> +	ret = HYPERVISOR_memory_op(XENMEM_memory_map, &memmap);
> +	if (ret == -ENOSYS) {
> +		unsigned long max_pfn = min(MAX_DOMAIN_PAGES,
> +					    xen_start_info->nr_pages);
> +		memmap.nr_entries = 1;
> +		map[0].addr = 0ULL;
> +		map[0].size = PFN_PHYS(max_pfn);
> +		/* 8MB slack (to balance backend allocations). */
> +		map[0].size += 8ULL << 20;
> +		map[0].type = E820_RAM;
> +	} else if (ret < 0)
> +		return ret;
> +
> +	*nr_entries = memmap.nr_entries;
> +	return 0;
> +}
> +
> +static int __init xen_get_memory_map(struct e820entry *map, unsigned *nr_entries)
> +{
> +	if (xen_initial_domain())
> +		return xen_get_memory_map_dom0(map, nr_entries);
> +	else
> +		return xen_get_memory_map_domu(map, nr_entries);
> +}
> +
>  static void __init xen_add_extra_mem(u64 start, u64 size)
>  {
>  	unsigned long pfn;
> @@ -319,42 +404,25 @@ static void xen_align_and_add_e820_region(u64 start, u64 size, int type)
>  char * __init xen_memory_setup(void)
>  {
>  	static struct e820entry map[E820MAX] __initdata;
> +	unsigned map_nr_entries = E820MAX;
>  
>  	unsigned long max_pfn = xen_start_info->nr_pages;
>  	unsigned long long mem_end;
>  	int rc;
> -	struct xen_memory_map memmap;
>  	unsigned long max_pages;
>  	unsigned long last_pfn = 0;
>  	unsigned long extra_pages = 0;
>  	unsigned long populated;
>  	int i;
> -	int op;
>  
>  	max_pfn = min(MAX_DOMAIN_PAGES, max_pfn);
>  	mem_end = PFN_PHYS(max_pfn);
>  
> -	memmap.nr_entries = E820MAX;
> -	set_xen_guest_handle(memmap.buffer, map);
> -
> -	op = xen_initial_domain() ?
> -		XENMEM_machine_memory_map :
> -		XENMEM_memory_map;
> -	rc = HYPERVISOR_memory_op(op, &memmap);
> -	if (rc == -ENOSYS) {
> -		BUG_ON(xen_initial_domain());
> -		memmap.nr_entries = 1;
> -		map[0].addr = 0ULL;
> -		map[0].size = mem_end;
> -		/* 8MB slack (to balance backend allocations). */
> -		map[0].size += 8ULL << 20;
> -		map[0].type = E820_RAM;
> -		rc = 0;
> -	}
> +	rc = xen_get_memory_map(map, &map_nr_entries);
>  	BUG_ON(rc);
>  
>  	/* Make sure the Xen-supplied memory map is well-ordered. */
> -	sanitize_e820_map(map, memmap.nr_entries, &memmap.nr_entries);
> +	sanitize_e820_map(map, map_nr_entries, &map_nr_entries);
>  
>  	max_pages = xen_get_max_pages();
>  	if (max_pages > max_pfn)
> @@ -366,12 +434,12 @@ char * __init xen_memory_setup(void)
>  	 * this are first released.
>  	 */
>  	xen_released_pages = xen_set_identity_and_release(
> -		map, memmap.nr_entries, max_pfn);
> +		map, map_nr_entries, max_pfn);
>  
>  	/*
>  	 * Populate back the non-RAM pages and E820 gaps that had been
>  	 * released. */
> -	populated = xen_populate_chunk(map, memmap.nr_entries,
> +	populated = xen_populate_chunk(map, map_nr_entries,
>  			max_pfn, &last_pfn, xen_released_pages);
>  
>  	xen_released_pages -= populated;
> @@ -395,7 +463,7 @@ char * __init xen_memory_setup(void)
>  	extra_pages = min(EXTRA_MEM_RATIO * min(max_pfn, PFN_DOWN(MAXMEM)),
>  			  extra_pages);
>  	i = 0;
> -	while (i < memmap.nr_entries) {
> +	while (i < map_nr_entries) {
>  		u64 addr = map[i].addr;
>  		u64 size = map[i].size;
>  		u32 type = map[i].type;

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