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Subject[PATCH 7/8] xen/mmu: Introduce IDENTITY_FRAME_BIT
Date
We tack on the IDENTITY_FRAME_BIT on all PFNs which have been
elected during the E820 parsing to be identity mapping.

This way, in case a freak occurs such that pfn_to_mfn(pfn)==pfn
for non-identity PFNs we can guard against that and not consider
it a 1-1 mapping.

Also this will allows us to leverage this and tack on _PAGE_IOMAP
on any page that has IDENTITY_FRAME_BIT set (see:
"xen/mmu: Set _PAGE_IOMAP if PFN is in identity P2M.").

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
arch/x86/include/asm/xen/page.h | 6 +++++-
arch/x86/xen/mmu.c | 11 ++++++++---
arch/x86/xen/setup.c | 2 +-
3 files changed, 14 insertions(+), 5 deletions(-)
diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
index be671f6..a1e4ce8 100644
--- a/arch/x86/include/asm/xen/page.h
+++ b/arch/x86/include/asm/xen/page.h
@@ -30,6 +30,7 @@ typedef struct xpaddr {
/**** MACHINE <-> PHYSICAL CONVERSION MACROS ****/
#define INVALID_P2M_ENTRY (~0UL)
#define FOREIGN_FRAME_BIT (1UL<<31)
+#define IDENTITY_FRAME_BIT (1UL<<30)
#define FOREIGN_FRAME(m) ((m) | FOREIGN_FRAME_BIT)

/* Maximum amount of memory we can handle in a domain in pages */
@@ -52,9 +53,12 @@ static inline unsigned long pfn_to_mfn(unsigned long pfn)

mfn = get_phys_to_machine(pfn);

- if (mfn != INVALID_P2M_ENTRY)
+ if (mfn != INVALID_P2M_ENTRY) {
mfn &= ~FOREIGN_FRAME_BIT;

+ if (mfn & IDENTITY_FRAME_BIT)
+ mfn &= ~IDENTITY_FRAME_BIT;
+ }
return mfn;
}

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index d98bd43..d470435 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -425,10 +425,10 @@ unsigned long get_phys_to_machine(unsigned long pfn)
* would be wrong.
*/
if (p2m_top[topidx] == p2m_mid_identity)
- return pfn;
+ return pfn | IDENTITY_FRAME_BIT;

if (p2m_top[topidx][mididx] == p2m_identity)
- return pfn;
+ return pfn | IDENTITY_FRAME_BIT;

return p2m_top[topidx][mididx][idx];
}
@@ -546,7 +546,7 @@ 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.
*/
- if (pfn == mfn) {
+ if (mfn != INVALID_P2M_ENTRY && (mfn & IDENTITY_FRAME_BIT)) {
if (p2m_top[topidx] == p2m_mid_identity)
return 1;
if (p2m_top[topidx][mididx] == p2m_identity)
@@ -2834,7 +2834,12 @@ static int p2m_dump_show(struct seq_file *m, void *v)
} else if (p2m_top[topidx][mididx] == p2m_identity) {
lvl = 1; type = TYPE_IDENTITY;
} else if (p2m_top[topidx][mididx][idx] == pfn) {
+ lvl = 2; type = TYPE_PFN;
+ } else if (p2m_top[topidx][mididx][idx] ==
+ (pfn | IDENTITY_FRAME_BIT)) {
lvl = 2; type = TYPE_IDENTITY;
+ } else if (p2m_top[topidx][mididx][idx] != pfn) {
+ lvl = 2; type = TYPE_PFN;
} else if (p2m_top[topidx] == NULL) {
lvl = 0; type = TYPE_UNKN;
} else if (p2m_top[topidx][mididx] == NULL) {
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 643b3fc..35b3b4d 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -168,7 +168,7 @@ static unsigned long __init xen_set_identity(const struct e820map *e820)
}

for (pfn = PFN_UP(last); pfn < PFN_DOWN(end); pfn++)
- __set_phys_to_machine(pfn, pfn);
+ __set_phys_to_machine(pfn, pfn | IDENTITY_FRAME_BIT);
identity += pfn - PFN_UP(last);

last = end;
--
1.7.1


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