[PATCH v4 0/2] x86/hvm/viridian: APIC assist

[PATCH v4 0/2] x86/hvm/viridian: APIC assist

[Paul Durrant]

This patch series enables use of the 'APIC assist' enlightenment in Xen.

See section 13.3.4.1 of the Microsoft Hypervisor Top Level Function
Specification v4.0b at:

https://msdn.microsoft.com/en-us/virtualization/hyperv_on_windows/develop/tlfs

for more information.

Patch #1 modifies the viridian code to keep the guest APIC assist pages
mapped for the lifetime of the domain (and incorporates a straightforward
data-structure change).

Patch #2 adds a new viridian code and a configuration option to the
toolstack that, when enabled, allows the local APIC emulation to make use
the APIC assist pages.


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[PATCH v4 1/2] x86/hvm/viridian: keep APIC assist page mapped...

[Paul Durrant]

... for the lifetime of the domain.

If Xen is to make use of the APIC assist enlightenment then a persistent
mapping needs to be kept, rather than the temporary one which is currently
used only to initialize the page content.

This patch also adds a comment block at the top of the source with
information on the latest version of the spec. from Microsoft and the
current URL where it may be found.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Cc: Keir Fraser <keir@xen.org>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
---

v4:
 - Added missing teardown required if the MSR is re-written.

v2:
 - Re-instated warning if the initialization of an APIC assist page fails.
 - Added up-to-date information about the viridian specification to the
   comment block at the top of the source.
---
 xen/arch/x86/hvm/hvm.c             |  2 +
 xen/arch/x86/hvm/viridian.c        | 77 ++++++++++++++++++++++++++++----------
 xen/include/asm-x86/hvm/viridian.h |  8 +++-
 3 files changed, 66 insertions(+), 21 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 4ea51d7..f446ee4 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2606,6 +2606,8 @@ int hvm_vcpu_initialise(struct vcpu *v)
 
 void hvm_vcpu_destroy(struct vcpu *v)
 {
+    viridian_vcpu_deinit(v);
+
     hvm_all_ioreq_servers_remove_vcpu(v->domain, v);
 
     if ( hvm_altp2m_supported() )
diff --git a/xen/arch/x86/hvm/viridian.c b/xen/arch/x86/hvm/viridian.c
index 1ee22aa..b809118 100644
--- a/xen/arch/x86/hvm/viridian.c
+++ b/xen/arch/x86/hvm/viridian.c
@@ -1,7 +1,12 @@
 /******************************************************************************
  * viridian.c
  *
- * An implementation of the Viridian hypercall interface.
+ * An implementation of some Viridian enlightenments. See Microsoft's
+ * Hypervisor Top Level Functional Specification (v4.0b) at:
+ *
+ * https://msdn.microsoft.com/en-us/virtualization/hyperv_on_windows/develop/tlfs
+ *
+ * for more information.
  */
 
 #include <xen/sched.h>
@@ -163,7 +168,7 @@ static void dump_apic_assist(const struct vcpu *v)
 {
     const union viridian_apic_assist *aa;
 
-    aa = &v->arch.hvm_vcpu.viridian.apic_assist;
+    aa = &v->arch.hvm_vcpu.viridian.apic_assist.msr;
 
     printk(XENLOG_G_INFO "%pv: VIRIDIAN APIC_ASSIST: enabled: %x pfn: %lx\n",
            v, aa->fields.enabled, (unsigned long)aa->fields.pfn);
@@ -217,9 +222,9 @@ static void enable_hypercall_page(struct domain *d)
 static void initialize_apic_assist(struct vcpu *v)
 {
     struct domain *d = v->domain;
-    unsigned long gmfn = v->arch.hvm_vcpu.viridian.apic_assist.fields.pfn;
+    unsigned long gmfn = v->arch.hvm_vcpu.viridian.apic_assist.msr.fields.pfn;
     struct page_info *page = get_page_from_gfn(d, gmfn, NULL, P2M_ALLOC);
-    uint8_t *p;
+    void *va;
 
     /*
      * We don't yet make use of the APIC assist page but by setting
@@ -227,25 +232,49 @@ static void initialize_apic_assist(struct vcpu *v)
      * bound to support the MSR. We therefore do just enough to keep windows
      * happy.
      *
-     * See http://msdn.microsoft.com/en-us/library/ff538657%28VS.85%29.aspx for
-     * details of how Windows uses the page.
+     * See section 13.3.4.1 of the specification for details of this
+     * enlightenment.
      */
 
-    if ( !page || !get_page_type(page, PGT_writable_page) )
+    if ( !page )
+        goto fail;
+
+    if ( !get_page_type(page, PGT_writable_page) )
     {
-        if ( page )
-            put_page(page);
-        gdprintk(XENLOG_WARNING, "Bad GMFN %lx (MFN %lx)\n", gmfn,
-                 page ? page_to_mfn(page) : INVALID_MFN);
-        return;
+        put_page(page);
+        goto fail;
     }
 
-    p = __map_domain_page(page);
+    va = __map_domain_page_global(page);
+    if ( !va )
+    {
+        put_page_and_type(page);
+        goto fail;
+    }
 
-    *(u32 *)p = 0;
+    *(uint32_t *)va = 0;
 
-    unmap_domain_page(p);
+    v->arch.hvm_vcpu.viridian.apic_assist.page = page;
+    v->arch.hvm_vcpu.viridian.apic_assist.va = va;
+    return;
+
+ fail:
+    gdprintk(XENLOG_WARNING, "Bad GMFN %lx (MFN %lx)\n", gmfn,
+             page ? page_to_mfn(page) : INVALID_MFN);
+}
+
+static void teardown_apic_assist(struct vcpu *v)
+{
+    struct page_info *page = v->arch.hvm_vcpu.viridian.apic_assist.page;
+    void *va = v->arch.hvm_vcpu.viridian.apic_assist.va;
 
+    if ( !va )
+        return;
+
+    v->arch.hvm_vcpu.viridian.apic_assist.va = NULL;
+    v->arch.hvm_vcpu.viridian.apic_assist.page = NULL;
+
+    unmap_domain_page_global(va);
     put_page_and_type(page);
 }
 
@@ -374,9 +403,10 @@ int wrmsr_viridian_regs(uint32_t idx, uint64_t val)
 
     case VIRIDIAN_MSR_APIC_ASSIST:
         perfc_incr(mshv_wrmsr_apic_msr);
-        v->arch.hvm_vcpu.viridian.apic_assist.raw = val;
+        teardown_apic_assist(v); /* release any previous mapping */
+        v->arch.hvm_vcpu.viridian.apic_assist.msr.raw = val;
         dump_apic_assist(v);
-        if (v->arch.hvm_vcpu.viridian.apic_assist.fields.enabled)
+        if ( v->arch.hvm_vcpu.viridian.apic_assist.msr.fields.enabled )
             initialize_apic_assist(v);
         break;
 
@@ -485,7 +515,7 @@ int rdmsr_viridian_regs(uint32_t idx, uint64_t *val)
 
     case VIRIDIAN_MSR_APIC_ASSIST:
         perfc_incr(mshv_rdmsr_apic_msr);
-        *val = v->arch.hvm_vcpu.viridian.apic_assist.raw;
+        *val = v->arch.hvm_vcpu.viridian.apic_assist.msr.raw;
         break;
 
     case VIRIDIAN_MSR_REFERENCE_TSC:
@@ -521,6 +551,11 @@ int rdmsr_viridian_regs(uint32_t idx, uint64_t *val)
     return 1;
 }
 
+void viridian_vcpu_deinit(struct vcpu *v)
+{
+    teardown_apic_assist(v);
+}
+
 static DEFINE_PER_CPU(cpumask_t, ipi_cpumask);
 
 int viridian_hypercall(struct cpu_user_regs *regs)
@@ -721,7 +756,7 @@ static int viridian_save_vcpu_ctxt(struct domain *d, hvm_domain_context_t *h)
     for_each_vcpu( d, v ) {
         struct hvm_viridian_vcpu_context ctxt;
 
-        ctxt.apic_assist = v->arch.hvm_vcpu.viridian.apic_assist.raw;
+        ctxt.apic_assist = v->arch.hvm_vcpu.viridian.apic_assist.msr.raw;
 
         if ( hvm_save_entry(VIRIDIAN_VCPU, v->vcpu_id, h, &ctxt) != 0 )
             return 1;
@@ -747,7 +782,9 @@ static int viridian_load_vcpu_ctxt(struct domain *d, hvm_domain_context_t *h)
     if ( hvm_load_entry(VIRIDIAN_VCPU, h, &ctxt) != 0 )
         return -EINVAL;
 
-    v->arch.hvm_vcpu.viridian.apic_assist.raw = ctxt.apic_assist;
+    v->arch.hvm_vcpu.viridian.apic_assist.msr.raw = ctxt.apic_assist;
+    if ( v->arch.hvm_vcpu.viridian.apic_assist.msr.fields.enabled )
+        initialize_apic_assist(v);
 
     return 0;
 }
diff --git a/xen/include/asm-x86/hvm/viridian.h b/xen/include/asm-x86/hvm/viridian.h
index c4319d7..ee3a120 100644
--- a/xen/include/asm-x86/hvm/viridian.h
+++ b/xen/include/asm-x86/hvm/viridian.h
@@ -21,7 +21,11 @@ union viridian_apic_assist
 
 struct viridian_vcpu
 {
-    union viridian_apic_assist apic_assist;
+    struct {
+        union viridian_apic_assist msr;
+        struct page_info *page;
+        void *va;
+    } apic_assist;
 };
 
 union viridian_guest_os_id
@@ -117,6 +121,8 @@ viridian_hypercall(struct cpu_user_regs *regs);
 void viridian_time_ref_count_freeze(struct domain *d);
 void viridian_time_ref_count_thaw(struct domain *d);
 
+void viridian_vcpu_deinit(struct vcpu *v);
+
 #endif /* __ASM_X86_HVM_VIRIDIAN_H__ */
 
 /*
-- 
2.1.4


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[PATCH v4 2/2] x86/hvm/viridian: Enable APIC assist enlightenment

[Paul Durrant]

This patch adds code to enable the APIC assist enlightenment which,
under certain conditions, means that the guest can avoid an EOI of
the local APIC and thereby avoid a VMEXIT.

Use of the enlightenment by the hypervisor is under control of the
toolstack, and is added to the default set.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Cc: Keir Fraser <keir@xen.org>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
---

v4:
 - Re-worded xl.cfg text and added missing LIBXL_HAVE_ definition

v3:
 - Re-instated read-modify-write for forwards compatibility
 - Fix a coding style issue

v2:
 - Removed some code duplication and unnecessary read-modify-write
   operations on the APIC assist word.
 - Stated in the xl.cfg text that the enlightenment has no effect if
   posted interrupts are in use.
 - Added the enlightenment to the default set.
---
 docs/man/xl.cfg.pod.5              | 12 +++++++-
 tools/libxl/libxl.h                |  6 ++++
 tools/libxl/libxl_dom.c            |  4 +++
 tools/libxl/libxl_types.idl        |  1 +
 xen/arch/x86/hvm/viridian.c        | 59 ++++++++++++++++++++++++++++++++++----
 xen/arch/x86/hvm/vlapic.c          | 58 +++++++++++++++++++++++++++++++++----
 xen/include/asm-x86/hvm/viridian.h |  5 ++++
 xen/include/public/hvm/params.h    |  7 ++++-
 8 files changed, 139 insertions(+), 13 deletions(-)

diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
index 56b1117..abf638c 100644
--- a/docs/man/xl.cfg.pod.5
+++ b/docs/man/xl.cfg.pod.5
@@ -1484,10 +1484,20 @@ This set incorporates use of hypercalls for remote TLB flushing.
 This enlightenment may improve performance of Windows guests running
 on hosts with higher levels of (physical) CPU contention.
 
+=item B<apic_assist>
+
+This set incorporates use of the APIC assist page to avoid EOI of
+the local APIC.
+This enlightenment may improve performance of guests that make use of
+per-vcpu event channel upcall vectors.
+Note that this enlightenment will have no effect if the guest is
+using APICv posted interrupts.
+
 =item B<defaults>
 
 This is a special value that enables the default set of groups, which
-is currently the B<base>, B<freq> and B<time_ref_count> groups.
+is currently the B<base>, B<freq>, B<time_ref_count> and B<apic_assist>
+groups.
 
 =item B<all>
 
diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index f9e3ef5..055a7b4 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -218,6 +218,12 @@
 #define LIBXL_HAVE_SOFT_RESET 1
 
 /*
+ * LIBXL_HAVE_APIC_ASSIST indicates that the 'apic_assist' value
+ * is present in the viridian enlightenment enumeration.
+ */
+#define LIBXL_HAVE_APIC_ASSIST 1
+
+/*
  * libxl ABI compatibility
  *
  * The only guarantee which libxl makes regarding ABI compatibility
diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
index b825b98..09d3bca 100644
--- a/tools/libxl/libxl_dom.c
+++ b/tools/libxl/libxl_dom.c
@@ -211,6 +211,7 @@ static int hvm_set_viridian_features(libxl__gc *gc, uint32_t domid,
         libxl_bitmap_set(&enlightenments, LIBXL_VIRIDIAN_ENLIGHTENMENT_BASE);
         libxl_bitmap_set(&enlightenments, LIBXL_VIRIDIAN_ENLIGHTENMENT_FREQ);
         libxl_bitmap_set(&enlightenments, LIBXL_VIRIDIAN_ENLIGHTENMENT_TIME_REF_COUNT);
+        libxl_bitmap_set(&enlightenments, LIBXL_VIRIDIAN_ENLIGHTENMENT_APIC_ASSIST);
     }
 
     libxl_for_each_set_bit(v, info->u.hvm.viridian_enable) {
@@ -253,6 +254,9 @@ static int hvm_set_viridian_features(libxl__gc *gc, uint32_t domid,
     if (libxl_bitmap_test(&enlightenments, LIBXL_VIRIDIAN_ENLIGHTENMENT_HCALL_REMOTE_TLB_FLUSH))
         mask |= HVMPV_hcall_remote_tlb_flush;
 
+    if (libxl_bitmap_test(&enlightenments, LIBXL_VIRIDIAN_ENLIGHTENMENT_APIC_ASSIST))
+        mask |= HVMPV_apic_assist;
+
     if (mask != 0 &&
         xc_hvm_param_set(CTX->xch,
                          domid,
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index 632c009..e3be957 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -221,6 +221,7 @@ libxl_viridian_enlightenment = Enumeration("viridian_enlightenment", [
     (2, "time_ref_count"),
     (3, "reference_tsc"),
     (4, "hcall_remote_tlb_flush"),
+    (5, "apic_assist"),
     ])
 
 libxl_hdtype = Enumeration("hdtype", [
diff --git a/xen/arch/x86/hvm/viridian.c b/xen/arch/x86/hvm/viridian.c
index b809118..e45dcb7 100644
--- a/xen/arch/x86/hvm/viridian.c
+++ b/xen/arch/x86/hvm/viridian.c
@@ -227,11 +227,6 @@ static void initialize_apic_assist(struct vcpu *v)
     void *va;
 
     /*
-     * We don't yet make use of the APIC assist page but by setting
-     * the CPUID3A_MSR_APIC_ACCESS bit in CPUID leaf 40000003 we are duty
-     * bound to support the MSR. We therefore do just enough to keep windows
-     * happy.
-     *
      * See section 13.3.4.1 of the specification for details of this
      * enlightenment.
      */
@@ -256,6 +251,7 @@ static void initialize_apic_assist(struct vcpu *v)
 
     v->arch.hvm_vcpu.viridian.apic_assist.page = page;
     v->arch.hvm_vcpu.viridian.apic_assist.va = va;
+    v->arch.hvm_vcpu.viridian.apic_assist.vector = -1;
     return;
 
  fail:
@@ -263,6 +259,59 @@ static void initialize_apic_assist(struct vcpu *v)
              page ? page_to_mfn(page) : INVALID_MFN);
 }
 
+static uint32_t *get_apic_assist_word(struct vcpu *v)
+{
+    if ( !(viridian_feature_mask(v->domain) & HVMPV_apic_assist) )
+        return NULL;
+
+    return v->arch.hvm_vcpu.viridian.apic_assist.va;
+}
+
+void viridian_start_apic_assist(struct vcpu *v, int vector)
+{
+    uint32_t *va = get_apic_assist_word(v);
+
+    if ( !va )
+        return;
+
+    /*
+     * If there is already an assist pending then something has gone
+     * wrong and the VM will most likely hang so force a crash now
+     * to make the problem clear.
+     */
+    if ( v->arch.hvm_vcpu.viridian.apic_assist.vector >= 0 )
+        domain_crash(v->domain);
+
+    v->arch.hvm_vcpu.viridian.apic_assist.vector = vector;
+    *va |= 1u;
+}
+
+bool_t viridian_complete_apic_assist(struct vcpu *v, int *vector)
+{
+    uint32_t *va = get_apic_assist_word(v);
+
+    if ( !va )
+        return 0;
+
+    if ( *va & 1u )
+        return 0; /* Interrupt not yet processed by the guest */
+
+    *vector = v->arch.hvm_vcpu.viridian.apic_assist.vector;
+    v->arch.hvm_vcpu.viridian.apic_assist.vector = -1;
+    return 1;
+}
+
+void viridian_abort_apic_assist(struct vcpu *v)
+{
+    uint32_t *va = get_apic_assist_word(v);
+
+    if ( !va )
+        return;
+
+    *va &= ~1u;
+    v->arch.hvm_vcpu.viridian.apic_assist.vector = -1;
+}
+
 static void teardown_apic_assist(struct vcpu *v)
 {
     struct page_info *page = v->arch.hvm_vcpu.viridian.apic_assist.page;
diff --git a/xen/arch/x86/hvm/vlapic.c b/xen/arch/x86/hvm/vlapic.c
index 01a8430..aac4263 100644
--- a/xen/arch/x86/hvm/vlapic.c
+++ b/xen/arch/x86/hvm/vlapic.c
@@ -38,6 +38,7 @@
 #include <asm/hvm/support.h>
 #include <asm/hvm/vmx/vmx.h>
 #include <asm/hvm/nestedhvm.h>
+#include <asm/hvm/viridian.h>
 #include <public/hvm/ioreq.h>
 #include <public/hvm/params.h>
 
@@ -95,6 +96,18 @@ static int vlapic_find_highest_vector(const void *bitmap)
     return (fls(word[word_offset*4]) - 1) + (word_offset * 32);
 }
 
+static int vlapic_find_lowest_vector(const void *bitmap)
+{
+    const uint32_t *word = bitmap;
+    unsigned int word_offset;
+
+    /* Work forwards through the bitmap (first 32-bit word in every four). */
+    for ( word_offset = 0; word_offset < NR_VECTORS / 32; word_offset++)
+        if ( word[word_offset * 4] )
+            return (ffs(word[word_offset * 4]) - 1) + (word_offset * 32);
+
+    return -1;
+}
 
 /*
  * IRR-specific bitmap update & search routines.
@@ -1157,7 +1170,7 @@ int vlapic_virtual_intr_delivery_enabled(void)
 int vlapic_has_pending_irq(struct vcpu *v)
 {
     struct vlapic *vlapic = vcpu_vlapic(v);
-    int irr, isr;
+    int irr, vector, isr;
 
     if ( !vlapic_enabled(vlapic) )
         return -1;
@@ -1170,10 +1183,27 @@ int vlapic_has_pending_irq(struct vcpu *v)
          !nestedhvm_vcpu_in_guestmode(v) )
         return irr;
 
+    /*
+     * If APIC assist was used then there may have been no EOI so
+     * we need to clear the requisite bit from the ISR here, before
+     * comparing with the IRR.
+     */
+    if ( viridian_complete_apic_assist(v, &vector) &&
+         vector != -1 )
+        vlapic_clear_vector(vector, &vlapic->regs->data[APIC_ISR]);
+
     isr = vlapic_find_highest_isr(vlapic);
     isr = (isr != -1) ? isr : 0;
     if ( (isr & 0xf0) >= (irr & 0xf0) )
+    {
+        /*
+         * There's already a higher priority vector pending so
+         * we need to abort any previous APIC assist to ensure there
+         * is an EOI.
+         */
+        viridian_abort_apic_assist(v);
         return -1;
+    }
 
     return irr;
 }
@@ -1181,13 +1211,29 @@ int vlapic_has_pending_irq(struct vcpu *v)
 int vlapic_ack_pending_irq(struct vcpu *v, int vector, bool_t force_ack)
 {
     struct vlapic *vlapic = vcpu_vlapic(v);
+    int isr;
 
-    if ( force_ack || !vlapic_virtual_intr_delivery_enabled() )
-    {
-        vlapic_set_vector(vector, &vlapic->regs->data[APIC_ISR]);
-        vlapic_clear_irr(vector, vlapic);
-    }
+    if ( !force_ack &&
+         vlapic_virtual_intr_delivery_enabled() )
+        return 1;
+
+    if ( vlapic_test_vector(vector, &vlapic->regs->data[APIC_TMR]) )
+        goto done;
+
+    isr = vlapic_find_lowest_vector(&vlapic->regs->data[APIC_ISR]);
+    if ( isr >= 0 && isr < vector )
+        goto done;
+
+    /*
+     * This vector is edge triggered and there are no lower priority
+     * vectors pending, so we can use APIC assist to avoid exiting
+     * for EOI.
+     */
+    viridian_start_apic_assist(v, vector);
 
+done:
+    vlapic_set_vector(vector, &vlapic->regs->data[APIC_ISR]);
+    vlapic_clear_irr(vector, vlapic);
     return 1;
 }
 
diff --git a/xen/include/asm-x86/hvm/viridian.h b/xen/include/asm-x86/hvm/viridian.h
index ee3a120..e0a523e 100644
--- a/xen/include/asm-x86/hvm/viridian.h
+++ b/xen/include/asm-x86/hvm/viridian.h
@@ -25,6 +25,7 @@ struct viridian_vcpu
         union viridian_apic_assist msr;
         struct page_info *page;
         void *va;
+        int vector;
     } apic_assist;
 };
 
@@ -123,6 +124,10 @@ void viridian_time_ref_count_thaw(struct domain *d);
 
 void viridian_vcpu_deinit(struct vcpu *v);
 
+void viridian_start_apic_assist(struct vcpu *v, int vector);
+bool_t viridian_complete_apic_assist(struct vcpu *v, int *vector);
+void viridian_abort_apic_assist(struct vcpu *v);
+
 #endif /* __ASM_X86_HVM_VIRIDIAN_H__ */
 
 /*
diff --git a/xen/include/public/hvm/params.h b/xen/include/public/hvm/params.h
index 73d4718..e69c72c 100644
--- a/xen/include/public/hvm/params.h
+++ b/xen/include/public/hvm/params.h
@@ -115,12 +115,17 @@
 #define _HVMPV_hcall_remote_tlb_flush 4
 #define HVMPV_hcall_remote_tlb_flush (1 << _HVMPV_hcall_remote_tlb_flush)
 
+/* Use APIC assist */
+#define _HVMPV_apic_assist 5
+#define HVMPV_apic_assist (1 << _HVMPV_apic_assist)
+
 #define HVMPV_feature_mask \
         (HVMPV_base_freq | \
          HVMPV_no_freq | \
          HVMPV_time_ref_count | \
          HVMPV_reference_tsc | \
-         HVMPV_hcall_remote_tlb_flush)
+         HVMPV_hcall_remote_tlb_flush | \
+         HVMPV_apic_assist)
 
 #endif
 
-- 
2.1.4


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Re: [PATCH v4 1/2] x86/hvm/viridian: keep APIC assist page mapped...

[Andrew Cooper]

On 17/03/16 08:37, Paul Durrant wrote:
> ... for the lifetime of the domain.
>
> If Xen is to make use of the APIC assist enlightenment then a persistent
> mapping needs to be kept, rather than the temporary one which is currently
> used only to initialize the page content.
>
> This patch also adds a comment block at the top of the source with
> information on the latest version of the spec. from Microsoft and the
> current URL where it may be found.
>
> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> Cc: Keir Fraser <keir@xen.org>
> Cc: Jan Beulich <jbeulich@suse.com>
> Cc: Andrew Cooper <andrew.cooper3@citrix.com>

By the looks of it, this patch textually depends on your Viridian TLB fixes?

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

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Re: [PATCH v4 1/2] x86/hvm/viridian: keep APIC assist page mapped...

[Paul Durrant]

> -----Original Message-----
> From: Andrew Cooper [mailto:andrew.cooper3@citrix.com]
> Sent: 17 March 2016 10:51
> To: Paul Durrant; xen-devel@lists.xenproject.org
> Cc: Keir (Xen.org); Jan Beulich
> Subject: Re: [PATCH v4 1/2] x86/hvm/viridian: keep APIC assist page
> mapped...
> 
> On 17/03/16 08:37, Paul Durrant wrote:
> > ... for the lifetime of the domain.
> >
> > If Xen is to make use of the APIC assist enlightenment then a persistent
> > mapping needs to be kept, rather than the temporary one which is
> currently
> > used only to initialize the page content.
> >
> > This patch also adds a comment block at the top of the source with
> > information on the latest version of the spec. from Microsoft and the
> > current URL where it may be found.
> >
> > Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> > Cc: Keir Fraser <keir@xen.org>
> > Cc: Jan Beulich <jbeulich@suse.com>
> > Cc: Andrew Cooper <andrew.cooper3@citrix.com>
> 
> By the looks of it, this patch textually depends on your Viridian TLB fixes?
> 

Yes, this series is based on my branch including the fix, so it should be applied afterwards.

> Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

Thanks,

  Paul

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Re: [PATCH v4 1/2] x86/hvm/viridian: keep APIC assist page mapped...

[Jan Beulich]

>>> On 17.03.16 at 09:37, <paul.durrant@citrix.com> wrote:
> +static void teardown_apic_assist(struct vcpu *v)
> +{
> +    struct page_info *page = v->arch.hvm_vcpu.viridian.apic_assist.page;
> +    void *va = v->arch.hvm_vcpu.viridian.apic_assist.va;
>  
> +    if ( !va )
> +        return;
> +
> +    v->arch.hvm_vcpu.viridian.apic_assist.va = NULL;
> +    v->arch.hvm_vcpu.viridian.apic_assist.page = NULL;
> +
> +    unmap_domain_page_global(va);
>      put_page_and_type(page);
>  }

The apic_assist.page field is needed only here, and is redundant
with the va being stored (from which it can be derived via
domain_page_map_to_mfn()). Please let's avoid needlessly
growing struct vcpu.

Jan


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Re: [PATCH v4 1/2] x86/hvm/viridian: keep APIC assist page mapped...

[Paul Durrant]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@suse.com]
> Sent: 17 March 2016 11:59
> To: Paul Durrant
> Cc: Andrew Cooper; xen-devel@lists.xenproject.org; Keir (Xen.org)
> Subject: Re: [PATCH v4 1/2] x86/hvm/viridian: keep APIC assist page
> mapped...
> 
> >>> On 17.03.16 at 09:37, <paul.durrant@citrix.com> wrote:
> > +static void teardown_apic_assist(struct vcpu *v)
> > +{
> > +    struct page_info *page = v->arch.hvm_vcpu.viridian.apic_assist.page;
> > +    void *va = v->arch.hvm_vcpu.viridian.apic_assist.va;
> >
> > +    if ( !va )
> > +        return;
> > +
> > +    v->arch.hvm_vcpu.viridian.apic_assist.va = NULL;
> > +    v->arch.hvm_vcpu.viridian.apic_assist.page = NULL;
> > +
> > +    unmap_domain_page_global(va);
> >      put_page_and_type(page);
> >  }
> 
> The apic_assist.page field is needed only here, and is redundant
> with the va being stored (from which it can be derived via
> domain_page_map_to_mfn()). Please let's avoid needlessly
> growing struct vcpu.
> 

Ok. I'll drop it then.

  Paul

> Jan


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