[Xen-devel] [PATCH 02/27] xen: Allow unprivileged Xen domains to create iomap pages

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

From: Alex Nixon <alex.nixon@xxxxxxxxxx>

PV DomU domains are allowed to map hardware MFNs for PCI passthrough,
but are not generally allowed to map raw machine pages.  In particular,
various pieces of code try to map DMI and ACPI tables in the ISA ROM
range.  We disallow _PAGE_IOMAP for those mappings, so that they are
redirected to a set of local zeroed pages we reserve for that purpose.

Signed-off-by: Alex Nixon <alex.nixon@xxxxxxxxxx>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
---
 arch/x86/xen/enlighten.c |    6 +++---
 arch/x86/xen/mmu.c       |   18 +++++++++++++++---
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index f673cd8..0605f19 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -998,11 +998,11 @@ asmlinkage void __init xen_start_kernel(void)
 
        /* Prevent unwanted bits from being set in PTEs. */
        __supported_pte_mask &= ~_PAGE_GLOBAL;
-       if (xen_initial_domain())
-               __supported_pte_mask |= _PAGE_IOMAP;
-       else
+       if (!xen_initial_domain())
                __supported_pte_mask &= ~(_PAGE_PWT | _PAGE_PCD);
 
+       __supported_pte_mask |= _PAGE_IOMAP;
+
        /* Don't do the full vcpu_info placement stuff until we have a
           possible map and a non-dummy shared_info. */
        per_cpu(xen_vcpu, 0) = &HYPERVISOR_shared_info->vcpu_info[0];
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 0a0cd61..58af0b0 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -49,6 +49,7 @@
 #include <asm/mmu_context.h>
 #include <asm/setup.h>
 #include <asm/paravirt.h>
+#include <asm/e820.h>
 #include <asm/linkage.h>
 
 #include <asm/xen/hypercall.h>
@@ -398,7 +399,7 @@ static bool xen_page_pinned(void *ptr)
 
 static bool xen_iomap_pte(pte_t pte)
 {
-       return xen_initial_domain() && (pte_flags(pte) & _PAGE_IOMAP);
+       return pte_flags(pte) & _PAGE_IOMAP;
 }
 
 static void xen_set_iomap_pte(pte_t *ptep, pte_t pteval)
@@ -600,10 +601,21 @@ PV_CALLEE_SAVE_REGS_THUNK(xen_pgd_val);
 
 pte_t xen_make_pte(pteval_t pte)
 {
-       if (unlikely(xen_initial_domain() && (pte & _PAGE_IOMAP)))
+       phys_addr_t addr = (pte & PTE_PFN_MASK);
+
+       /*
+        * 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
+       } else {
+               pte &= ~_PAGE_IOMAP;
                pte = pte_pfn_to_mfn(pte);
+       }
 
        return native_make_pte(pte);
 }
-- 
1.6.0.6


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