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.durr...@citrix.com>
Cc: Ian Jackson <ian.jack...@eu.citrix.com>
Cc: Stefano Stabellini <stefano.stabell...@eu.citrix.com>
Cc: Wei Liu <wei.l...@citrix.com>
Cc: Keir Fraser <k...@xen.org>
Cc: Jan Beulich <jbeul...@suse.com>
Cc: Andrew Cooper <andrew.coop...@citrix.com>
---
v6:
- Addressed various comments from Jan
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 | 62 ++++++++++++++++++++++++++++++++++----
xen/arch/x86/hvm/vlapic.c | 60 ++++++++++++++++++++++++++++++++----
xen/include/asm-x86/hvm/hvm.h | 3 ++
xen/include/asm-x86/hvm/viridian.h | 5 +++
xen/include/public/hvm/params.h | 7 ++++-
9 files changed, 146 insertions(+), 14 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 f726df1..410320c 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.
*/
@@ -254,7 +249,15 @@ static void initialize_apic_assist(struct vcpu *v)
*(uint32_t *)va = 0;
- v->arch.hvm_vcpu.viridian.apic_assist.va = va;
+ if ( viridian_feature_mask(v->domain) & HVMPV_apic_assist )
+ {
+ v->arch.hvm_vcpu.viridian.apic_assist.va = va;
+ v->arch.hvm_vcpu.viridian.apic_assist.vector = -1;
+ return;
+ }
+
+ unmap_domain_page_global(va);
+ put_page_and_type(page);
return;
fail:
@@ -278,6 +281,53 @@ static void teardown_apic_assist(struct vcpu *v)
put_page_and_type(page);
}
+void viridian_start_apic_assist(struct vcpu *v, int vector)
+{
+ uint32_t *va = v->arch.hvm_vcpu.viridian.apic_assist.va;
+
+ 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;
+}
+
+int viridian_complete_apic_assist(struct vcpu *v)
+{
+ uint32_t *va = v->arch.hvm_vcpu.viridian.apic_assist.va;
+ int vector;
+
+ if ( !va )
+ return -1;
+
+ if ( *va & 1u )
+ return -1; /* 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 vector;
+}
+
+void viridian_abort_apic_assist(struct vcpu *v)
+{
+ uint32_t *va = v->arch.hvm_vcpu.viridian.apic_assist.va;
+
+ if ( !va )
+ return;
+
+ *va &= ~1u;
+ v->arch.hvm_vcpu.viridian.apic_assist.vector = -1;
+}
+
static void update_reference_tsc(struct domain *d, bool_t initialize)
{
unsigned long gmfn = d->arch.hvm_domain.viridian.reference_tsc.fields.pfn;
diff --git a/xen/arch/x86/hvm/vlapic.c b/xen/arch/x86/hvm/vlapic.c
index 01a8430..4af2107 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.
+ */
+ vector = viridian_complete_apic_assist(v);
+ if ( 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 +1211,31 @@ 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 there's no chance of using APIC assist then bail now. */
+ if ( !has_viridian_apic_assist(v->domain) ||
+ 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/hvm.h b/xen/include/asm-x86/hvm/hvm.h
index b8ab5b1..751ab1c 100644
--- a/xen/include/asm-x86/hvm/hvm.h
+++ b/xen/include/asm-x86/hvm/hvm.h
@@ -402,6 +402,9 @@ static inline unsigned long hvm_get_shadow_gs_base(struct
vcpu *v)
#define has_viridian_time_ref_count(d) \
(is_viridian_domain(d) && (viridian_feature_mask(d) &
HVMPV_time_ref_count))
+#define has_viridian_apic_assist(d) \
+ (is_viridian_domain(d) && (viridian_feature_mask(d) & HVMPV_apic_assist))
+
void hvm_hypervisor_cpuid_leaf(uint32_t sub_idx,
uint32_t *eax, uint32_t *ebx,
uint32_t *ecx, uint32_t *edx);
diff --git a/xen/include/asm-x86/hvm/viridian.h
b/xen/include/asm-x86/hvm/viridian.h
index 19ecc06..7f281b2 100644
--- a/xen/include/asm-x86/hvm/viridian.h
+++ b/xen/include/asm-x86/hvm/viridian.h
@@ -24,6 +24,7 @@ struct viridian_vcpu
struct {
union viridian_apic_assist msr;
void *va;
+ int vector;
} apic_assist;
};
@@ -122,6 +123,10 @@ 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);
+int viridian_complete_apic_assist(struct vcpu *v);
+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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