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|
/*
* Xen leaves the responsibility for maintaining p2m mappings to the
* guests themselves, but it must also access and update the p2m array
* during suspend/resume when all the pages are reallocated.
*
* The p2m table is logically a flat array, but we implement it as a
* three-level tree to allow the address space to be sparse.
*
* Xen
* |
* p2m_top p2m_top_mfn
* / \ / \
* p2m_mid p2m_mid p2m_mid_mfn p2m_mid_mfn
* / \ / \ / /
* p2m p2m p2m p2m p2m p2m p2m ...
*
* The p2m_mid_mfn pages are mapped by p2m_top_mfn_p.
*
* The p2m_top and p2m_top_mfn levels are limited to 1 page, so the
* maximum representable pseudo-physical address space is:
* P2M_TOP_PER_PAGE * P2M_MID_PER_PAGE * P2M_PER_PAGE pages
*
* P2M_PER_PAGE depends on the architecture, as a mfn is always
* unsigned long (8 bytes on 64-bit, 4 bytes on 32), leading to
* 512 and 1024 entries respectively.
*
* In short, these structures contain the Machine Frame Number (MFN) of the PFN.
*
* However not all entries are filled with MFNs. Specifically for all other
* leaf entries, or for the top root, or middle one, for which there is a void
* entry, we assume it is "missing". So (for example)
* pfn_to_mfn(0x90909090)=INVALID_P2M_ENTRY.
*
* We also have the possibility of setting 1-1 mappings on certain regions, so
* that:
* 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
* get the PFN value to match the MFN.
*
* For this to work efficiently we have one new page p2m_identity and
* allocate (via reserved_brk) any other pages we need to cover the sides
* (1GB or 4MB boundary violations). All entries in p2m_identity are set to
* INVALID_P2M_ENTRY type (Xen toolstack only recognizes that and MFNs,
* no other fancy value).
*
* On lookup we spot that the entry points to p2m_identity and return the
* identity value instead of dereferencing and returning INVALID_P2M_ENTRY.
* If the entry points to an allocated page, we just proceed as before and
* return the PFN. If the PFN has IDENTITY_FRAME_BIT set we unmask that in
* appropriate functions (pfn_to_mfn).
*
* The reason for having the IDENTITY_FRAME_BIT instead of just returning the
* PFN is that we could find ourselves where pfn_to_mfn(pfn)==pfn for a
* non-identity pfn. To protect ourselves against we elect to set (and get) the
* IDENTITY_FRAME_BIT on all identity mapped PFNs.
*
* This simplistic diagram is used to explain the more subtle piece of code.
* There is also a digram of the P2M at the end that can help.
* Imagine your E820 looking as so:
*
* 1GB 2GB
* /-------------------+---------\/----\ /----------\ /---+-----\
* | System RAM | Sys RAM ||ACPI| | reserved | | Sys RAM |
* \-------------------+---------/\----/ \----------/ \---+-----/
* ^- 1029MB ^- 2001MB
*
* [1029MB = 263424 (0x40500), 2001MB = 512256 (0x7D100),
* 2048MB = 524288 (0x80000)]
*
* And dom0_mem=max:3GB,1GB is passed in to the guest, meaning memory past 1GB
* is actually not present (would have to kick the balloon driver to put it in).
*
* When we are told to set the PFNs for identity mapping (see patch: "xen/setup:
* Set identity mapping for non-RAM E820 and E820 gaps.") we pass in the start
* 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).
*
* 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.
* Each entry in the allocate page is "missing" (points to p2m_missing).
*
* 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
* 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"
* values) and assign them to p2m[1][2] and p2m[1][488] respectively.
*
* At this point we would at minimum reserve_brk one page, but could be up to
* three. Each call to set_phys_range_identity has at maximum a three page
* cost. If we were to query the P2M at this stage, all those entries from
* start PFN through end PFN (so 1029MB -> 2001MB) would return
* INVALID_P2M_ENTRY ("missing").
*
* 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
* 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
* that page (which covers 512 PFNs) and set the appropriate PFN with
* IDENTITY_FRAME_BIT. In our example 263424 and 512256 end up there, and we
* set from p2m[1][2][256->511] and p2m[1][488][0->256] with
* IDENTITY_FRAME_BIT set.
*
* All other regions that are void (or not filled) either point to p2m_missing
* (considered missing) or have the default value of INVALID_P2M_ENTRY (also
* 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."
*
* This is what the p2m ends up looking (for the E820 above) with this
* fabulous drawing:
*
* p2m /--------------\
* /-----\ | &mfn_list[0],| /-----------------\
* | 0 |------>| &mfn_list[1],| /---------------\ | ~0, ~0, .. |
* |-----| | ..., ~0, ~0 | | ~0, ~0, [x]---+----->| IDENTITY [@256] |
* | 1 |---\ \--------------/ | [p2m_identity]+\ | IDENTITY [@257] |
* |-----| \ | [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 |
* \-----------------/ \------------/
*
* where ~0 is INVALID_P2M_ENTRY. IDENTITY is (PFN | IDENTITY_BIT)
*/
#include <linux/init.h>
#include <linux/module.h>
#include <linux/list.h>
#include <linux/hash.h>
#include <linux/sched.h>
#include <linux/seq_file.h>
#include <asm/cache.h>
#include <asm/setup.h>
#include <asm/xen/page.h>
#include <asm/xen/hypercall.h>
#include <asm/xen/hypervisor.h>
#include <xen/balloon.h>
#include <xen/grant_table.h>
#include "multicalls.h"
#include "xen-ops.h"
static void __init m2p_override_init(void);
unsigned long xen_max_p2m_pfn __read_mostly;
#define P2M_PER_PAGE (PAGE_SIZE / sizeof(unsigned long))
#define P2M_MID_PER_PAGE (PAGE_SIZE / sizeof(unsigned long *))
#define P2M_TOP_PER_PAGE (PAGE_SIZE / sizeof(unsigned long **))
#define MAX_P2M_PFN (P2M_TOP_PER_PAGE * P2M_MID_PER_PAGE * P2M_PER_PAGE)
/* Placeholders for holes in the address space */
static RESERVE_BRK_ARRAY(unsigned long, p2m_missing, P2M_PER_PAGE);
static RESERVE_BRK_ARRAY(unsigned long *, p2m_mid_missing, P2M_MID_PER_PAGE);
static RESERVE_BRK_ARRAY(unsigned long, p2m_mid_missing_mfn, P2M_MID_PER_PAGE);
static RESERVE_BRK_ARRAY(unsigned long **, p2m_top, P2M_TOP_PER_PAGE);
static RESERVE_BRK_ARRAY(unsigned long, p2m_top_mfn, P2M_TOP_PER_PAGE);
static RESERVE_BRK_ARRAY(unsigned long *,
|