VMX: use a single, global APIC access page

The address of this page is used by the CPU only to recognize when to
access the virtual APIC page instead. No accesses would ever go to this
page. It only needs to be present in the (CPU) page tables so that
address translation will produce its address as result for respective
accesses.

By making this page global, we also eliminate the need to refcount it,
or to assign it to any domain in the first place.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Acked-by: Tim Deegan <tim@xen.org>

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index dde4f3b70d5355220994fbcd665f9f357ebcd58c..1450fd19915391a6ca0a4a46a00a1a18d8bbc90d 100644 (file)
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -66,8 +66,7 @@ boolean_param("force-ept", opt_force_ept);
 static void vmx_ctxt_switch_from(struct vcpu *v);
 static void vmx_ctxt_switch_to(struct vcpu *v);
 
-static int  vmx_alloc_vlapic_mapping(struct domain *d);
-static void vmx_free_vlapic_mapping(struct domain *d);
+static int alloc_vlapic_mapping(void);
 static void vmx_install_vlapic_mapping(struct vcpu *v);
 static void vmx_update_guest_cr(struct vcpu *v, unsigned int cr,
                                 unsigned int flags);
@@ -78,6 +77,8 @@ static int vmx_msr_read_intercept(unsigned int msr, uint64_t *msr_content);
 static int vmx_msr_write_intercept(unsigned int msr, uint64_t msr_content);
 static void vmx_invlpg(struct vcpu *v, unsigned long linear);
 
+static mfn_t __read_mostly apic_access_mfn = INVALID_MFN_INITIALIZER;
+
 /* Values for domain's ->arch.hvm_domain.pi_ops.flags. */
 #define PI_CSW_FROM (1u << 0)
 #define PI_CSW_TO   (1u << 1)
@@ -401,7 +402,6 @@ static int vmx_domain_initialise(struct domain *d)
         .to   = vmx_ctxt_switch_to,
         .tail = vmx_do_resume,
     };
-    int rc;
 
     d->arch.ctxt_switch = &csw;
 
@@ -411,28 +411,22 @@ static int vmx_domain_initialise(struct domain *d)
      */
     d->arch.hvm.vmx.exec_sp = is_hardware_domain(d) || opt_ept_exec_sp;
 
-    if ( !has_vlapic(d) )
-        return 0;
-
-    if ( (rc = vmx_alloc_vlapic_mapping(d)) != 0 )
-        return rc;
-
     return 0;
 }
 
-static void vmx_domain_relinquish_resources(struct domain *d)
+static void domain_creation_finished(struct domain *d)
 {
-    if ( !has_vlapic(d) )
+    gfn_t gfn = gaddr_to_gfn(APIC_DEFAULT_PHYS_BASE);
+    uint8_t ipat;
+
+    if ( !has_vlapic(d) || mfn_eq(apic_access_mfn, INVALID_MFN) )
         return;
 
-    vmx_free_vlapic_mapping(d);
-}
+    ASSERT(epte_get_entry_emt(d, gfn_x(gfn), apic_access_mfn, 0, &ipat,
+                              true) == MTRR_TYPE_WRBACK);
+    ASSERT(ipat);
 
-static void domain_creation_finished(struct domain *d)
-{
-    if ( has_vlapic(d) && !mfn_eq(d->arch.hvm.vmx.apic_access_mfn, _mfn(0)) &&
-         set_mmio_p2m_entry(d, gaddr_to_gfn(APIC_DEFAULT_PHYS_BASE),
-                            d->arch.hvm.vmx.apic_access_mfn, PAGE_ORDER_4K) )
+    if ( set_mmio_p2m_entry(d, gfn, apic_access_mfn, PAGE_ORDER_4K) )
         domain_crash(d);
 }
 
@@ -2415,7 +2409,6 @@ static struct hvm_function_table __initdata vmx_function_table = {
     .cpu_up_prepare       = vmx_cpu_up_prepare,
     .cpu_dead             = vmx_cpu_dead,
     .domain_initialise    = vmx_domain_initialise,
-    .domain_relinquish_resources = vmx_domain_relinquish_resources,
     .domain_creation_finished = domain_creation_finished,
     .vcpu_initialise      = vmx_vcpu_initialise,
     .vcpu_destroy         = vmx_vcpu_destroy,
@@ -2662,7 +2655,7 @@ const struct hvm_function_table * __init start_vmx(void)
 {
     set_in_cr4(X86_CR4_VMXE);
 
-    if ( vmx_vmcs_init() )
+    if ( vmx_vmcs_init() || alloc_vlapic_mapping() )
     {
         printk("VMX: failed to initialise.\n");
         return NULL;
@@ -3236,7 +3229,7 @@ gp_fault:
     return X86EMUL_EXCEPTION;
 }
 
-static int vmx_alloc_vlapic_mapping(struct domain *d)
+static int __init alloc_vlapic_mapping(void)
 {
     struct page_info *pg;
     mfn_t mfn;
@@ -3244,52 +3237,34 @@ static int vmx_alloc_vlapic_mapping(struct domain *d)
     if ( !cpu_has_vmx_virtualize_apic_accesses )
         return 0;
 
-    pg = alloc_domheap_page(d, MEMF_no_refcount);
+    pg = alloc_domheap_page(NULL, 0);
     if ( !pg )
         return -ENOMEM;
 
-    if ( !get_page_and_type(pg, d, PGT_writable_page) )
-    {
-        /*
-         * The domain can't possibly know about this page yet, so failure
-         * here is a clear indication of something fishy going on.
-         */
-        domain_crash(d);
-        return -ENODATA;
-    }
+    /*
+     * Signal to shadow code that this page cannot be refcounted. This also
+     * makes epte_get_entry_emt() recognize this page as "special".
+     */
+    page_suppress_refcounting(pg);
 
     mfn = page_to_mfn(pg);
     clear_domain_page(mfn);
-    d->arch.hvm.vmx.apic_access_mfn = mfn;
+    apic_access_mfn = mfn;
 
     return 0;
 }
 
-static void vmx_free_vlapic_mapping(struct domain *d)
-{
-    mfn_t mfn = d->arch.hvm.vmx.apic_access_mfn;
-
-    d->arch.hvm.vmx.apic_access_mfn = _mfn(0);
-    if ( !mfn_eq(mfn, _mfn(0)) )
-    {
-        struct page_info *pg = mfn_to_page(mfn);
-
-        put_page_alloc_ref(pg);
-        put_page_and_type(pg);
-    }
-}
-
 static void vmx_install_vlapic_mapping(struct vcpu *v)
 {
     paddr_t virt_page_ma, apic_page_ma;
 
-    if ( mfn_eq(v->domain->arch.hvm.vmx.apic_access_mfn, _mfn(0)) )
+    if ( !has_vlapic(v->domain) || mfn_eq(apic_access_mfn, INVALID_MFN) )
         return;
 
     ASSERT(cpu_has_vmx_virtualize_apic_accesses);
 
     virt_page_ma = page_to_maddr(vcpu_vlapic(v)->regs_page);
-    apic_page_ma = mfn_to_maddr(v->domain->arch.hvm.vmx.apic_access_mfn);
+    apic_page_ma = mfn_to_maddr(apic_access_mfn);
 
     vmx_vmcs_enter(v);
     __vmwrite(VIRTUAL_APIC_PAGE_ADDR, virt_page_ma);

diff --git a/xen/arch/x86/mm/shadow/set.c b/xen/arch/x86/mm/shadow/set.c
index fff4d1633c79de892e4eaeab69f45693412aafd5..7c952749942137ad0ff55d49af19e1a7fba427a5 100644 (file)
--- a/xen/arch/x86/mm/shadow/set.c
+++ b/xen/arch/x86/mm/shadow/set.c
@@ -94,6 +94,15 @@ shadow_get_page_from_l1e(shadow_l1e_t sl1e, struct domain *d, p2m_type_t type)
     ASSERT(!sh_l1e_is_magic(sl1e));
     ASSERT(shadow_mode_refcounts(d));
 
+    /*
+     * Check whether refcounting is suppressed on this page. For example,
+     * VMX'es APIC access MFN is just a surrogate page.  It doesn't actually
+     * get accessed, and hence there's no need to refcount it.
+     */
+    mfn = shadow_l1e_get_mfn(sl1e);
+    if ( mfn_valid(mfn) && page_refcounting_suppressed(mfn_to_page(mfn)) )
+        return 0;
+
     res = get_page_from_l1e(sl1e, d, d);
 
     /*

diff --git a/xen/arch/x86/mm/shadow/types.h b/xen/arch/x86/mm/shadow/types.h
index 814a4018535a274aa29d3a8ab2604c2c9ee86db0..6970e7d6ea4afc92a8ddebcd545ed352bcaf2360 100644 (file)
--- a/xen/arch/x86/mm/shadow/types.h
+++ b/xen/arch/x86/mm/shadow/types.h
@@ -276,9 +276,16 @@ int shadow_set_l4e(struct domain *d, shadow_l4e_t *sl4e,
 static void inline
 shadow_put_page_from_l1e(shadow_l1e_t sl1e, struct domain *d)
 {
+    mfn_t mfn = shadow_l1e_get_mfn(sl1e);
+
     if ( !shadow_mode_refcounts(d) )
         return;
 
+    if ( mfn_valid(mfn) &&
+         /* See the respective comment in shadow_get_page_from_l1e(). */
+         page_refcounting_suppressed(mfn_to_page(mfn)) )
+        return;
+
     put_page_from_l1e(sl1e, d);
 }
 

diff --git a/xen/include/asm-x86/hvm/vmx/vmcs.h b/xen/include/asm-x86/hvm/vmx/vmcs.h
index 8073af323b968632803a1a41578772ef59a49461..03c9ccf627ab5339bde093e81f8c96c6f7179d0d 100644 (file)
--- a/xen/include/asm-x86/hvm/vmx/vmcs.h
+++ b/xen/include/asm-x86/hvm/vmx/vmcs.h
@@ -58,7 +58,6 @@ struct ept_data {
 #define _VMX_DOMAIN_PML_ENABLED    0
 #define VMX_DOMAIN_PML_ENABLED     (1ul << _VMX_DOMAIN_PML_ENABLED)
 struct vmx_domain {
-    mfn_t apic_access_mfn;
     /* VMX_DOMAIN_* */
     unsigned int status;
 

diff --git a/xen/include/asm-x86/mm.h b/xen/include/asm-x86/mm.h
index 56d7a71a24a4f8abcfb836a4a267dfcfd7de5205..80b0ccffaacb92afb2b903f2dc1cc1b98070061e 100644 (file)
--- a/xen/include/asm-x86/mm.h
+++ b/xen/include/asm-x86/mm.h
@@ -82,7 +82,7 @@
 #define PGC_state_offlined PG_mask(2, 9)
 #define PGC_state_free    PG_mask(3, 9)
 #define page_state_is(pg, st) (((pg)->count_info&PGC_state) == PGC_state_##st)
-/* Page is not reference counted */
+/* Page is not reference counted (see below for caveats) */
 #define _PGC_extra        PG_shift(10)
 #define PGC_extra         PG_mask(1, 10)
 
@@ -374,6 +374,24 @@ void zap_ro_mpt(mfn_t mfn);
 
 bool is_iomem_page(mfn_t mfn);
 
+/*
+ * Pages with no owner which may get passed to functions wanting to
+ * refcount them can be marked PGC_extra to bypass this refcounting (which
+ * would fail due to the lack of an owner).
+ *
+ * (For pages with owner PGC_extra has different meaning.)
+ */
+static inline void page_suppress_refcounting(struct page_info *pg)
+{
+   ASSERT(!page_get_owner(pg));
+   pg->count_info |= PGC_extra;
+}
+
+static inline bool page_refcounting_suppressed(const struct page_info *pg)
+{
+    return !page_get_owner(pg) && (pg->count_info & PGC_extra);
+}
+
 struct platform_bad_page {
     unsigned long mfn;
     unsigned int order;