Commit 250a41e0 authored by Konrad Rzeszutek Wilk's avatar Konrad Rzeszutek Wilk
Browse files

xen/p2m: Reuse existing P2M leafs if they are filled with 1:1 PFNs or INVALID. 



If P2M leaf is completly packed with INVALID_P2M_ENTRY or with
1:1 PFNs (so IDENTITY_FRAME type PFNs), we can swap the P2M leaf
with either a p2m_missing or p2m_identity respectively. The old
page (which was created via extend_brk or was grafted on from the
mfn_list) can be re-used for setting new PFNs.

This also means we can remove git commit:
5bc6f988
xen/p2m: Reserve 8MB of _brk space for P2M leafs when populating back
which tried to fix this.

and make the amount that is required to be reserved much smaller.

CC: stable@vger.kernel.org # for 3.5 only.
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent ca08649e

arch/x86/xen/p2m.c

+92 −3
Original line number Diff line number Diff line
@@ -196,9 +196,11 @@ RESERVE_BRK(p2m_mid_identity, 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.

 * But some machines can have 3GB I/O holes even. So lets reserve enough

 * for 4GB of I/O and E820 holes. */

RESERVE_BRK(p2m_populated, PMD_SIZE * 4);

 * Some machines can have 3GB I/O holes even. With early_can_reuse_p2m_middle

 * it can re-use Xen provided mfn_list array, so we only need to allocate at

 * most three P2M top nodes. */

RESERVE_BRK(p2m_populated, PAGE_SIZE * 3);



static inline unsigned p2m_top_index(unsigned long pfn)

{

	BUG_ON(pfn >= MAX_P2M_PFN);
@@ -575,12 +577,99 @@ static bool __init early_alloc_p2m(unsigned long pfn) 
	}

	return true;

}



/*

 * Skim over the P2M tree looking at pages that are either filled with

 * INVALID_P2M_ENTRY or with 1:1 PFNs. If found, re-use that page and

 * replace the P2M leaf with a p2m_missing or p2m_identity.

 * Stick the old page in the new P2M tree location.

 */

bool __init early_can_reuse_p2m_middle(unsigned long set_pfn, unsigned long set_mfn)

{

	unsigned topidx;

	unsigned mididx;

	unsigned ident_pfns;

	unsigned inv_pfns;

	unsigned long *p2m;

	unsigned long *mid_mfn_p;

	unsigned idx;

	unsigned long pfn;



	/* We only look when this entails a P2M middle layer */

	if (p2m_index(set_pfn))

		return false;



	for (pfn = 0; pfn <= MAX_DOMAIN_PAGES; pfn += P2M_PER_PAGE) {

		topidx = p2m_top_index(pfn);



		if (!p2m_top[topidx])

			continue;



		if (p2m_top[topidx] == p2m_mid_missing)

			continue;



		mididx = p2m_mid_index(pfn);

		p2m = p2m_top[topidx][mididx];

		if (!p2m)

			continue;



		if ((p2m == p2m_missing) || (p2m == p2m_identity))

			continue;



		if ((unsigned long)p2m == INVALID_P2M_ENTRY)

			continue;



		ident_pfns = 0;

		inv_pfns = 0;

		for (idx = 0; idx < P2M_PER_PAGE; idx++) {

			/* IDENTITY_PFNs are 1:1 */

			if (p2m[idx] == IDENTITY_FRAME(pfn + idx))

				ident_pfns++;

			else if (p2m[idx] == INVALID_P2M_ENTRY)

				inv_pfns++;

			else

				break;

		}

		if ((ident_pfns == P2M_PER_PAGE) || (inv_pfns == P2M_PER_PAGE))

			goto found;

	}

	return false;

found:

	/* Found one, replace old with p2m_identity or p2m_missing */

	p2m_top[topidx][mididx] = (ident_pfns ? p2m_identity : p2m_missing);

	/* And the other for save/restore.. */

	mid_mfn_p = p2m_top_mfn_p[topidx];

	/* NOTE: Even if it is a p2m_identity it should still be point to

	 * a page filled with INVALID_P2M_ENTRY entries. */

	mid_mfn_p[mididx] = virt_to_mfn(p2m_missing);



	/* Reset where we want to stick the old page in. */

	topidx = p2m_top_index(set_pfn);

	mididx = p2m_mid_index(set_pfn);



	/* This shouldn't happen */

	if (WARN_ON(p2m_top[topidx] == p2m_mid_missing))

		early_alloc_p2m(set_pfn);



	if (WARN_ON(p2m_top[topidx][mididx] != p2m_missing))

		return false;



	p2m_init(p2m);

	p2m_top[topidx][mididx] = p2m;

	mid_mfn_p = p2m_top_mfn_p[topidx];

	mid_mfn_p[mididx] = virt_to_mfn(p2m);



	return true;

}

bool __init early_set_phys_to_machine(unsigned long pfn, unsigned long mfn)

{

	if (unlikely(!__set_phys_to_machine(pfn, mfn)))  {

		if (!early_alloc_p2m(pfn))

			return false;



		if (early_can_reuse_p2m_middle(pfn, mfn))

			return __set_phys_to_machine(pfn, mfn);



		if (!early_alloc_p2m_middle(pfn, false /* boundary crossover OK!*/))

			return false;

CRA Git | Maintained and supported by SUSTech CRA and CCSE