[PATCH 3/9] x86/xen: compactly store large identity ranges in the p2m

From: David Vrabel
Date: Tue Apr 15 2014 - 10:17:54 EST

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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: David Vrabel <david.vrabel@xxxxxxxxxx>
---
arch/x86/xen/p2m.c | 155 +++++++++++++++++++++++++++++++++++-----------------
1 files changed, 105 insertions(+), 50 deletions(-)

diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 82c8c93..5d716f7 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -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
- * |-----| \ \-------------------->/---------------\ /-----------------\
- * | .. +->+ | [p2m_identity]+-->| ~0, ~0, ~0, ... |
- * \-----/ / | [p2m_identity]+-->| ..., ~0 |
- * / /---------------\ | .... | \-----------------/
- * / | IDENTITY[@0] | /-+-[x], ~0, ~0.. |
- * / | IDENTITY[@256]|<----/ \---------------/
- * / | ~0, ~0, .... |
- * | \---------------/
- * |
- * p2m_mid_missing p2m_missing
- * /-----------------\ /------------\
- * | [p2m_missing] +---->| ~0, ~0, ~0 |
- * | [p2m_missing] +---->| ..., ~0 |
- * \-----------------/ \------------/
+ * | 3 |-\ \ \\ p2m_identity [1]
+ * |-----| \ \-------------------->/---------------\ /-----------------\
+ * | .. |\ | | [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_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;

--
1.7.2.5

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Next message: David Vrabel: "[PATCH 9/9] x86: remove the Xen-specific _PAGE_IOMAP PTE flag"
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