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Commit 3cb83e46 authored by David Vrabel's avatar David Vrabel
Browse files

x86/xen: compactly store large identity ranges in the p2m 



Large (multi-GB) identity ranges currently require a unique middle page
(filled with p2m_identity entries) per 1 GB region.

Similar to the common p2m_mid_missing middle page for large missing
regions, introduce a p2m_mid_identity page (filled with p2m_identity
entries) which can be used instead.

set_phys_range_identity() thus only needs to allocate new middle pages
at the beginning and end of the range.

Signed-off-by: default avatarDavid Vrabel <david.vrabel@citrix.com>
Reviewed-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Tested-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent a9b5bff6

arch/x86/xen/p2m.c

+105 −50
Original line number Diff line number Diff line
@@ -36,7 +36,7 @@ 
 *  pfn_to_mfn(0xc0000)=0xc0000

 *

 * The benefit of this is, that we can assume for non-RAM regions (think

 * PCI BARs, or ACPI spaces), we can create mappings easily b/c we

 * PCI BARs, or ACPI spaces), we can create mappings easily because we

 * get the PFN value to match the MFN.

 *

 * For this to work efficiently we have one new page p2m_identity and
@@ -60,7 +60,7 @@ 
 * There is also a digram of the P2M at the end that can help.

 * Imagine your E820 looking as so:

 *

 *                    1GB                                           2GB

 *                    1GB                                           2GB    4GB

 * /-------------------+---------\/----\         /----------\    /---+-----\

 * | System RAM        | Sys RAM ||ACPI|         | reserved |    | Sys RAM |

 * \-------------------+---------/\----/         \----------/    \---+-----/
@@ -77,9 +77,8 @@ 
 * of the PFN and the end PFN (263424 and 512256 respectively). The first step

 * is to reserve_brk a top leaf page if the p2m[1] is missing. The top leaf page

 * covers 512^2 of page estate (1GB) and in case the start or end PFN is not

 * aligned on 512^2*PAGE_SIZE (1GB) we loop on aligned 1GB PFNs from start pfn

 * to end pfn.  We reserve_brk top leaf pages if they are missing (means they

 * point to p2m_mid_missing).

 * aligned on 512^2*PAGE_SIZE (1GB) we reserve_brk new middle and leaf pages as

 * required to split any existing p2m_mid_missing middle pages.

 *

 * With the E820 example above, 263424 is not 1GB aligned so we allocate a

 * reserve_brk page which will cover the PFNs estate from 0x40000 to 0x80000.
@@ -88,7 +87,7 @@ 
 * Next stage is to determine if we need to do a more granular boundary check

 * on the 4MB (or 2MB depending on architecture) off the start and end pfn's.

 * We check if the start pfn and end pfn violate that boundary check, and if

 * so reserve_brk a middle (p2m[x][y]) leaf page. This way we have a much finer

 * so reserve_brk a (p2m[x][y]) leaf page. This way we have a much finer

 * granularity of setting which PFNs are missing and which ones are identity.

 * In our example 263424 and 512256 both fail the check so we reserve_brk two

 * pages. Populate them with INVALID_P2M_ENTRY (so they both have "missing"
@@ -102,9 +101,10 @@ 
 *

 * The next step is to walk from the start pfn to the end pfn setting

 * the IDENTITY_FRAME_BIT on each PFN. This is done in set_phys_range_identity.

 * If we find that the middle leaf is pointing to p2m_missing we can swap it

 * over to p2m_identity - this way covering 4MB (or 2MB) PFN space.  At this

 * point we do not need to worry about boundary aligment (so no need to

 * If we find that the middle entry is pointing to p2m_missing we can swap it

 * over to p2m_identity - this way covering 4MB (or 2MB) PFN space (and

 * similarly swapping p2m_mid_missing for p2m_mid_identity for larger regions).

 * At this point we do not need to worry about boundary aligment (so no need to

 * reserve_brk a middle page, figure out which PFNs are "missing" and which

 * ones are identity), as that has been done earlier.  If we find that the

 * middle leaf is not occupied by p2m_identity or p2m_missing, we dereference
@@ -118,6 +118,9 @@ 
 * considered missing). In our case, p2m[1][2][0->255] and p2m[1][488][257->511]

 * contain the INVALID_P2M_ENTRY value and are considered "missing."

 *

 * Finally, the region beyond the end of of the E820 (4 GB in this example)

 * is set to be identity (in case there are MMIO regions placed here).

 *

 * This is what the p2m ends up looking (for the E820 above) with this

 * fabulous drawing:

 *
@@ -129,21 +132,27 @@ 
 *  |-----|    \                      | [p2m_identity]+\\    | ....            |

 *  |  2  |--\  \-------------------->|  ...          | \\   \----------------/

 *  |-----|   \                       \---------------/  \\

 *  |  3  |\   \                                          \\  p2m_identity

 *  |  3  |-\  \                                          \\  p2m_identity [1]

 *  |-----|  \  \-------------------->/---------------\   /-----------------\

 *  | ..  +->+                        | [p2m_identity]+-->| ~0, ~0, ~0, ... |

 *  \-----/ /                         | [p2m_identity]+-->| ..., ~0         |

 *         / /---------------\        | ....          |   \-----------------/

 *        /  | IDENTITY[@0]  |      /-+-[x], ~0, ~0.. |

 *       /   | IDENTITY[@256]|<----/  \---------------/

 *      /    | ~0, ~0, ....  |

 *     |     \---------------/

 *  | ..  |\  |                       | [p2m_identity]+-->| ~0, ~0, ~0, ... |

 *  \-----/ | |                       | [p2m_identity]+-->| ..., ~0         |

 *          | |                       | ....          |   \-----------------/

 *          | |                       +-[x], ~0, ~0.. +\

 *          | |                       \---------------/ \

 *          | |                                          \-> /---------------\

 *          | V  p2m_mid_missing       p2m_missing           | IDENTITY[@0]  |

 *          | /-----------------\     /------------\         | IDENTITY[@256]|

 *          | | [p2m_missing]   +---->| ~0, ~0, ...|         | ~0, ~0, ....  |

 *          | | [p2m_missing]   +---->| ..., ~0    |         \---------------/

 *          | | ...             |     \------------/

 *          | \-----------------/

 *          |

 *   p2m_mid_missing           p2m_missing

 * /-----------------\     /------------\

 * | [p2m_missing]   +---->| ~0, ~0, ~0 |

 * | [p2m_missing]   +---->| ..., ~0    |

 * \-----------------/     \------------/

 *          |     p2m_mid_identity

 *          |   /-----------------\

 *          \-->| [p2m_identity]  +---->[1]

 *              | [p2m_identity]  +---->[1]

 *              | ...             |

 *              \-----------------/

 *

 * where ~0 is INVALID_P2M_ENTRY. IDENTITY is (PFN | IDENTITY_BIT)

 */
@@ -187,13 +196,15 @@ static RESERVE_BRK_ARRAY(unsigned long, p2m_top_mfn, P2M_TOP_PER_PAGE); 
static RESERVE_BRK_ARRAY(unsigned long *, p2m_top_mfn_p, P2M_TOP_PER_PAGE);



static RESERVE_BRK_ARRAY(unsigned long, p2m_identity, P2M_PER_PAGE);

static RESERVE_BRK_ARRAY(unsigned long *, p2m_mid_identity, P2M_MID_PER_PAGE);

static RESERVE_BRK_ARRAY(unsigned long, p2m_mid_identity_mfn, P2M_MID_PER_PAGE);



RESERVE_BRK(p2m_mid, PAGE_SIZE * (MAX_DOMAIN_PAGES / (P2M_PER_PAGE * P2M_MID_PER_PAGE)));

RESERVE_BRK(p2m_mid_mfn, PAGE_SIZE * (MAX_DOMAIN_PAGES / (P2M_PER_PAGE * P2M_MID_PER_PAGE)));



/* We might hit two boundary violations at the start and end, at max each

 * boundary violation will require three middle nodes. */

RESERVE_BRK(p2m_mid_identity, PAGE_SIZE * 2 * 3);

RESERVE_BRK(p2m_mid_extra, PAGE_SIZE * 2 * 3);



/* When we populate back during bootup, the amount of pages can vary. The

 * max we have is seen is 395979, but that does not mean it can't be more.
@@ -242,20 +253,20 @@ static void p2m_top_mfn_p_init(unsigned long **top) 
		top[i] = p2m_mid_missing_mfn;

}



static void p2m_mid_init(unsigned long **mid)

static void p2m_mid_init(unsigned long **mid, unsigned long *leaf)

{

	unsigned i;



	for (i = 0; i < P2M_MID_PER_PAGE; i++)

		mid[i] = p2m_missing;

		mid[i] = leaf;

}



static void p2m_mid_mfn_init(unsigned long *mid)

static void p2m_mid_mfn_init(unsigned long *mid, unsigned long *leaf)

{

	unsigned i;



	for (i = 0; i < P2M_MID_PER_PAGE; i++)

		mid[i] = virt_to_mfn(p2m_missing);

		mid[i] = virt_to_mfn(leaf);

}



static void p2m_init(unsigned long *p2m)
@@ -286,7 +297,9 @@ void __ref xen_build_mfn_list_list(void) 
	/* Pre-initialize p2m_top_mfn to be completely missing */

	if (p2m_top_mfn == NULL) {

		p2m_mid_missing_mfn = extend_brk(PAGE_SIZE, PAGE_SIZE);

		p2m_mid_mfn_init(p2m_mid_missing_mfn);

		p2m_mid_mfn_init(p2m_mid_missing_mfn, p2m_missing);

		p2m_mid_identity_mfn = extend_brk(PAGE_SIZE, PAGE_SIZE);

		p2m_mid_mfn_init(p2m_mid_identity_mfn, p2m_identity);



		p2m_top_mfn_p = extend_brk(PAGE_SIZE, PAGE_SIZE);

		p2m_top_mfn_p_init(p2m_top_mfn_p);
@@ -295,7 +308,8 @@ void __ref xen_build_mfn_list_list(void) 
		p2m_top_mfn_init(p2m_top_mfn);

	} else {

		/* Reinitialise, mfn's all change after migration */

		p2m_mid_mfn_init(p2m_mid_missing_mfn);

		p2m_mid_mfn_init(p2m_mid_missing_mfn, p2m_missing);

		p2m_mid_mfn_init(p2m_mid_identity_mfn, p2m_identity);

	}



	for (pfn = 0; pfn < xen_max_p2m_pfn; pfn += P2M_PER_PAGE) {
@@ -327,7 +341,7 @@ void __ref xen_build_mfn_list_list(void) 
			 * it too late.

			 */

			mid_mfn_p = extend_brk(PAGE_SIZE, PAGE_SIZE);

			p2m_mid_mfn_init(mid_mfn_p);

			p2m_mid_mfn_init(mid_mfn_p, p2m_missing);



			p2m_top_mfn_p[topidx] = mid_mfn_p;

		}
@@ -365,16 +379,17 @@ void __init xen_build_dynamic_phys_to_machine(void) 


	p2m_missing = extend_brk(PAGE_SIZE, PAGE_SIZE);

	p2m_init(p2m_missing);

	p2m_identity = extend_brk(PAGE_SIZE, PAGE_SIZE);

	p2m_init(p2m_identity);



	p2m_mid_missing = extend_brk(PAGE_SIZE, PAGE_SIZE);

	p2m_mid_init(p2m_mid_missing);

	p2m_mid_init(p2m_mid_missing, p2m_missing);

	p2m_mid_identity = extend_brk(PAGE_SIZE, PAGE_SIZE);

	p2m_mid_init(p2m_mid_identity, p2m_identity);



	p2m_top = extend_brk(PAGE_SIZE, PAGE_SIZE);

	p2m_top_init(p2m_top);



	p2m_identity = extend_brk(PAGE_SIZE, PAGE_SIZE);

	p2m_init(p2m_identity);



	/*

	 * The domain builder gives us a pre-constructed p2m array in

	 * mfn_list for all the pages initially given to us, so we just
@@ -386,7 +401,7 @@ void __init xen_build_dynamic_phys_to_machine(void) 


		if (p2m_top[topidx] == p2m_mid_missing) {

			unsigned long **mid = extend_brk(PAGE_SIZE, PAGE_SIZE);

			p2m_mid_init(mid);

			p2m_mid_init(mid, p2m_missing);



			p2m_top[topidx] = mid;

		}
@@ -545,7 +560,7 @@ static bool alloc_p2m(unsigned long pfn) 
		if (!mid)

			return false;



		p2m_mid_init(mid);

		p2m_mid_init(mid, p2m_missing);



		if (cmpxchg(top_p, p2m_mid_missing, mid) != p2m_mid_missing)

			free_p2m_page(mid);
@@ -565,7 +580,7 @@ static bool alloc_p2m(unsigned long pfn) 
		if (!mid_mfn)

			return false;



		p2m_mid_mfn_init(mid_mfn);

		p2m_mid_mfn_init(mid_mfn, p2m_missing);



		missing_mfn = virt_to_mfn(p2m_mid_missing_mfn);

		mid_mfn_mfn = virt_to_mfn(mid_mfn);
@@ -649,7 +664,7 @@ static bool __init early_alloc_p2m_middle(unsigned long pfn) 
	if (mid == p2m_mid_missing) {

		mid = extend_brk(PAGE_SIZE, PAGE_SIZE);



		p2m_mid_init(mid);

		p2m_mid_init(mid, p2m_missing);



		p2m_top[topidx] = mid;
@@ -658,7 +673,7 @@ static bool __init early_alloc_p2m_middle(unsigned long pfn) 
	/* And the save/restore P2M tables.. */

	if (mid_mfn_p == p2m_mid_missing_mfn) {

		mid_mfn_p = extend_brk(PAGE_SIZE, PAGE_SIZE);

		p2m_mid_mfn_init(mid_mfn_p);

		p2m_mid_mfn_init(mid_mfn_p, p2m_missing);



		p2m_top_mfn_p[topidx] = mid_mfn_p;

		p2m_top_mfn[topidx] = virt_to_mfn(mid_mfn_p);
@@ -769,6 +784,24 @@ bool __init early_set_phys_to_machine(unsigned long pfn, unsigned long mfn) 


	return true;

}



static void __init early_split_p2m(unsigned long pfn)

{

	unsigned long mididx, idx;



	mididx = p2m_mid_index(pfn);

	idx = p2m_index(pfn);



	/*

	 * Allocate new middle and leaf pages if this pfn lies in the

	 * middle of one.

	 */

	if (mididx || idx)

		early_alloc_p2m_middle(pfn);

	if (idx)

		early_alloc_p2m(pfn, false);

}



unsigned long __init set_phys_range_identity(unsigned long pfn_s,

				      unsigned long pfn_e)

{
@@ -786,19 +819,27 @@ unsigned long __init set_phys_range_identity(unsigned long pfn_s, 
	if (pfn_e > MAX_P2M_PFN)

		pfn_e = MAX_P2M_PFN;



	for (pfn = (pfn_s & ~(P2M_MID_PER_PAGE * P2M_PER_PAGE - 1));

		pfn < ALIGN(pfn_e, (P2M_MID_PER_PAGE * P2M_PER_PAGE));

		pfn += P2M_MID_PER_PAGE * P2M_PER_PAGE)

	{

		WARN_ON(!early_alloc_p2m(pfn));

	}

	early_split_p2m(pfn_s);

	early_split_p2m(pfn_e);



	early_alloc_p2m_middle(pfn_s, true);

	early_alloc_p2m_middle(pfn_e, true);

	for (pfn = pfn_s; pfn < pfn_e;) {

		unsigned topidx = p2m_top_index(pfn);

		unsigned mididx = p2m_mid_index(pfn);



	for (pfn = pfn_s; pfn < pfn_e; pfn++)

		if (!__set_phys_to_machine(pfn, IDENTITY_FRAME(pfn)))

			break;

		pfn++;



		/*

		 * If the PFN was set to a middle or leaf identity

		 * page the remainder must also be identity, so skip

		 * ahead to the next middle or leaf entry.

		 */

		if (p2m_top[topidx] == p2m_mid_identity)

			pfn = ALIGN(pfn, P2M_MID_PER_PAGE * P2M_PER_PAGE);

		else if (p2m_top[topidx][mididx] == p2m_identity)

			pfn = ALIGN(pfn, P2M_PER_PAGE);

	}



	if (!WARN((pfn - pfn_s) != (pfn_e - pfn_s),

		"Identity mapping failed. We are %ld short of 1-1 mappings!\n",
@@ -828,8 +869,22 @@ bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn) 


	/* For sparse holes were the p2m leaf has real PFN along with

	 * PCI holes, stick in the PFN as the MFN value.

	 *

	 * set_phys_range_identity() will have allocated new middle

	 * and leaf pages as required so an existing p2m_mid_missing

	 * or p2m_missing mean that whole range will be identity so

	 * these can be switched to p2m_mid_identity or p2m_identity.

	 */

	if (mfn != INVALID_P2M_ENTRY && (mfn & IDENTITY_FRAME_BIT)) {

		if (p2m_top[topidx] == p2m_mid_identity)

			return true;



		if (p2m_top[topidx] == p2m_mid_missing) {

			WARN_ON(cmpxchg(&p2m_top[topidx], p2m_mid_missing,

					p2m_mid_identity) != p2m_mid_missing);

			return true;

		}



		if (p2m_top[topidx][mididx] == p2m_identity)

			return true;