[Xen-devel] [PATCH 2/3] x86/xen: do not use _PAGE_IOMAP PTE flag for I/O mappings

[David Vrabel <david.vrabel@xxxxxxxxxx>]

Since mfn_to_pfn() returns the correct PFN for identity mappings (as
used for MMIO regions), the use of _PAGE_IOMAP is not required in
pte_mfn_to_pfn().

Do not set the _PAGE_IOMAP flag in pte_pfn_to_mfn() and do not use it
in pte_mfn_to_pfn().

This will allow _PAGE_IOMAP to be removed, making it available for
future use.

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 arch/x86/xen/mmu.c |   48 ++++--------------------------------------------
 1 file changed, 4 insertions(+), 44 deletions(-)

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index e8a1201..90e1d44 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -399,38 +399,14 @@ static pteval_t pte_pfn_to_mfn(pteval_t val)
                if (unlikely(mfn == INVALID_P2M_ENTRY)) {
                        mfn = 0;
                        flags = 0;
-               } else {
-                       /*
-                        * Paramount to do this test _after_ the
-                        * INVALID_P2M_ENTRY as INVALID_P2M_ENTRY &
-                        * IDENTITY_FRAME_BIT resolves to true.
-                        */
-                       mfn &= ~FOREIGN_FRAME_BIT;
-                       if (mfn & IDENTITY_FRAME_BIT) {
-                               mfn &= ~IDENTITY_FRAME_BIT;
-                               flags |= _PAGE_IOMAP;
-                       }
-               }
+               } else
+                       mfn &= ~(FOREIGN_FRAME_BIT | IDENTITY_FRAME_BIT);
                val = ((pteval_t)mfn << PAGE_SHIFT) | flags;
        }
 
        return val;
 }
 
-static pteval_t iomap_pte(pteval_t val)
-{
-       if (val & _PAGE_PRESENT) {
-               unsigned long pfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
-               pteval_t flags = val & PTE_FLAGS_MASK;
-
-               /* We assume the pte frame number is a MFN, so
-                  just use it as-is. */
-               val = ((pteval_t)pfn << PAGE_SHIFT) | flags;
-       }
-
-       return val;
-}
-
 __visible pteval_t xen_pte_val(pte_t pte)
 {
        pteval_t pteval = pte.pte;
@@ -441,9 +417,6 @@ __visible pteval_t xen_pte_val(pte_t pte)
                pteval = (pteval & ~_PAGE_PAT) | _PAGE_PWT;
        }
 #endif
-       if (xen_initial_domain() && (pteval & _PAGE_IOMAP))
-               return pteval;
-
        return pte_mfn_to_pfn(pteval);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_pte_val);
@@ -481,7 +454,6 @@ void xen_set_pat(u64 pat)
 
 __visible pte_t xen_make_pte(pteval_t pte)
 {
-       phys_addr_t addr = (pte & PTE_PFN_MASK);
 #if 0
        /* If Linux is trying to set a WC pte, then map to the Xen WC.
         * If _PAGE_PAT is set, then it probably means it is really
@@ -496,19 +468,7 @@ __visible pte_t xen_make_pte(pteval_t pte)
                        pte = (pte & ~(_PAGE_PCD | _PAGE_PWT)) | _PAGE_PAT;
        }
 #endif
-       /*
-        * Unprivileged domains are allowed to do IOMAPpings for
-        * PCI passthrough, but not map ISA space.  The ISA
-        * mappings are just dummy local mappings to keep other
-        * parts of the kernel happy.
-        */
-       if (unlikely(pte & _PAGE_IOMAP) &&
-           (xen_initial_domain() || addr >= ISA_END_ADDRESS)) {
-               pte = iomap_pte(pte);
-       } else {
-               pte &= ~_PAGE_IOMAP;
-               pte = pte_pfn_to_mfn(pte);
-       }
+       pte = pte_pfn_to_mfn(pte);
 
        return native_make_pte(pte);
 }
@@ -2094,7 +2054,7 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t 
phys, pgprot_t prot)
 
        default:
                /* By default, set_fixmap is used for hardware mappings */
-               pte = mfn_pte(phys, __pgprot(pgprot_val(prot) | _PAGE_IOMAP));
+               pte = mfn_pte(phys, prot);
                break;
        }
 
-- 
1.7.10.4


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