From: Christian Ehrhardt <[EMAIL PROTECTED]>

This patch adds the guest handling for the magic page mechanism. A Hypervisor
can modify the device tree passed to the guest. Using that already existing
interface a guest can simply detect available hypervisor features and agree
on the supported ones using hypercalls.
In this example it is checked for the feature switch "feature,pv-magicpage"
in the hypervisor node and additional data which represents the size the
hypervisor requests in "data,pv-magicpage-size".
When the guest reads that data and wants to support it the memory is allocated
and passed to the hypervisor using the KVM_HCALL_RESERVE_MAGICPAGE hypercall.

Signed-off-by: Christian Ehrhardt <[EMAIL PROTECTED]>
---

[diffstat]
 arch/powerpc/kernel/kvm.c      |   53 +++++++++++++++++++++++++++++++++++++++++
 include/asm-powerpc/fixmap.h   |   10 ++++++-
 include/asm-powerpc/kvm_para.h |   26 ++++++++++++++++++++
 3 files changed, 88 insertions(+), 1 deletion(-)
[diff]

diff --git a/arch/powerpc/kernel/kvm.c b/arch/powerpc/kernel/kvm.c
--- a/arch/powerpc/kernel/kvm.c
+++ b/arch/powerpc/kernel/kvm.c
@@ -22,9 +22,62 @@
 #include <linux/percpu.h>
 #include <linux/mm.h>
 #include <linux/kvm_para.h>
+#include <linux/bootmem.h>
+#include <asm/fixmap.h>
+#include <asm/epapr_hcalls.h>
+
+/*
+ * this is guest memory granted to the hypervisor;
+ * the hypervisor can place data in this area and rewrite
+ * privileged instructions to read from this area without
+ * trapping.
+ * Only the Hypervisor needs to be aware of the structure layout
+ * which makes the guest more felxible - the guest only guarantees
+ * the size which is requested by the hypervisor and read from a
+ * device tree entry.
+ */
+static void *kvm_magicpage;
+
+static void __init kvmppc_register_magic_page(void)
+{
+       unsigned long gvaddr;
+       unsigned long gpaddr;
+       int size;
+       long err;
+
+       size = kvmppc_pv_read_data(KVM_PVDATA_MAGICPAGE_SIZE);
+       if (size < 0) {
+               printk(KERN_ERR "%s: couldn't read size for kvmppc style "
+                       "paravirtualization support (got %d)\n",
+                       __func__, size);
+               return;
+       }
+
+       /* FIXME Guest SMP needs that percpu which */
+       kvm_magicpage = alloc_bootmem(size);
+       if (!kvm_magicpage) {
+               printk(KERN_ERR "%s - failed to allocate %d bytes\n",
+                        __func__, size);
+               return;
+       }
+       gpaddr = (unsigned long)__pa(kvm_magicpage);
+       gvaddr = fix_to_virt(FIX_KVM_PV);
+
+       err = epapr_hypercall_2in_1out(KVM_HCALL_RESERVE_MAGICPAGE,
+                                       gvaddr, gpaddr);
+       if (err)
+               printk(KERN_ERR "%s: couldn't register pv mem\n", __func__);
+       else
+               printk(KERN_NOTICE "%s: registered %d bytes for pv mem support"
+                       " (gvaddr 0x%08lx gpaddr 0x%08lx)\n",
+                        __func__, size, gvaddr, gpaddr);
+}
 
 void __init kvm_guest_init(void)
 {
        if (!kvm_para_available())
                return;
+
+       if (kvm_para_has_feature(KVM_FEATURE_PPCPV_MAGICPAGE))
+               kvmppc_register_magic_page();
 }
diff --git a/include/asm-powerpc/fixmap.h b/include/asm-powerpc/fixmap.h
--- a/include/asm-powerpc/fixmap.h
+++ b/include/asm-powerpc/fixmap.h
@@ -36,7 +36,7 @@
  *
  * these 'compile-time allocated' memory buffers are
  * fixed-size 4k pages. (or larger if used with an increment
- * highger than 1) use fixmap_set(idx,phys) to associate
+ * higher than 1) use fixmap_set(idx,phys) to associate
  * physical memory with fixmap indices.
  *
  * TLB entries of such buffers will not be flushed across
@@ -44,6 +44,14 @@
  */
 enum fixed_addresses {
        FIX_HOLE,
+#ifdef CONFIG_KVM_GUEST
+       /*
+        * reserved virtual address space for paravirtualization - needs to be
+        *  <=32k away from base address 0 to be able to reach it with
+        * immediate addressing using base 0 instead of needing a register.
+        */
+       FIX_KVM_PV,
+#endif
 #ifdef CONFIG_HIGHMEM
        FIX_KMAP_BEGIN, /* reserved pte's for temporary kernel mappings */
        FIX_KMAP_END = FIX_KMAP_BEGIN+(KM_TYPE_NR*NR_CPUS)-1,
diff --git a/include/asm-powerpc/kvm_para.h b/include/asm-powerpc/kvm_para.h
--- a/include/asm-powerpc/kvm_para.h
+++ b/include/asm-powerpc/kvm_para.h
@@ -26,10 +26,18 @@
 
 #include <linux/of.h>
 
+#define KVM_HCALL_RESERVE_MAGICPAGE    0
+
+#define KVM_PVDATA_MAGICPAGE_SIZE      "data,pv-magicpage-size"
+
+/* List of PV features supported, returned as a bitfield */
+#define KVM_FEATURE_PPCPV_MAGICPAGE    0
+
 static struct kvmppc_para_features {
        char *dtcell;
        int feature;
 } para_features[] = {
+       { "feature,pv-magicpage", KVM_FEATURE_PPCPV_MAGICPAGE }
 };
 
 static inline int kvm_para_available(void)
@@ -67,6 +75,24 @@
        return features;
 }
 
+/* reads the specified data field out of the hypervisor node */
+static inline int kvmppc_pv_read_data(char *dtcell)
+{
+       struct device_node *dn;
+       const int *dtval;
+
+       dn = of_find_node_by_path("/hypervisor");
+       if (!dn)
+               return -EINVAL;
+
+       dtval = of_get_property(dn, dtcell, NULL);
+       of_node_put(dn);
+       if (dtval)
+               return *dtval;
+       else
+               return -EINVAL;
+}
+
 void kvm_guest_init(void);
 
 #endif /* __KERNEL__ */
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