[PATCHv2 1/7] apic: fix typo EIO_ACK -> EOI_ACK and document

[PATCHv2 1/7] apic: fix typo EIO_ACK -> EOI_ACK and document

[Michael S. Tsirkin]

Fix typo in the macro name and document the
reason it has this value. Update users.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 arch/x86/include/asm/apicdef.h         |    2 +-
 arch/x86/platform/visws/visws_quirks.c |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/apicdef.h b/arch/x86/include/asm/apicdef.h
index 134bba0..c46bb99 100644
--- a/arch/x86/include/asm/apicdef.h
+++ b/arch/x86/include/asm/apicdef.h
@@ -37,7 +37,7 @@
 #define		APIC_ARBPRI_MASK	0xFFu
 #define	APIC_PROCPRI	0xA0
 #define	APIC_EOI	0xB0
-#define		APIC_EIO_ACK		0x0
+#define		APIC_EOI_ACK		0x0 /* Docs say 0 for future compat. */
 #define	APIC_RRR	0xC0
 #define	APIC_LDR	0xD0
 #define		APIC_LDR_MASK		(0xFFu << 24)
diff --git a/arch/x86/platform/visws/visws_quirks.c b/arch/x86/platform/visws/visws_quirks.c
index c7abf13..94d8a39 100644
--- a/arch/x86/platform/visws/visws_quirks.c
+++ b/arch/x86/platform/visws/visws_quirks.c
@@ -445,7 +445,7 @@ static void ack_cobalt_irq(struct irq_data *data)
 
 	spin_lock_irqsave(&cobalt_lock, flags);
 	disable_cobalt_irq(data);
-	apic_write(APIC_EOI, APIC_EIO_ACK);
+	apic_write(APIC_EOI, APIC_EOI_ACK);
 	spin_unlock_irqrestore(&cobalt_lock, flags);
 }
 
-- 
MST

[PATCHv2 2/7] apic: use symbolic APIC_EOI_ACK

[Michael S. Tsirkin]

Use the symbol instead of hard-coded numbers,
now that the reason for the value is documented
where the constant is defined we don't need to
duplicate this explanation in code.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 arch/x86/include/asm/apic.h |    4 +---
 1 files changed, 1 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index d854101..a09e9ab 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -463,9 +463,7 @@ static inline void ack_APIC_irq(void)
 	 * ack_APIC_irq() actually gets compiled as a single instruction
 	 * ... yummie.
 	 */
-
-	/* Docs say use 0 for future compatibility */
-	apic_write(APIC_EOI, 0);
+	apic_write(APIC_EOI, APIC_EOI_ACK);
 }
 
 static inline unsigned default_get_apic_id(unsigned long x)
-- 
MST

[PATCHv2 3/7] x86: add apic->eoi_write callback

[Michael S. Tsirkin]

Add eoi_write callback so that kvm can override
eoi accesses without touching the rest of the apic.
As a side-effect, this will enable a micro-optimization
for apics using msr.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 arch/x86/include/asm/apic.h           |   15 ++++++++++++++-
 arch/x86/kernel/apic/apic_flat_64.c   |    2 ++
 arch/x86/kernel/apic/apic_noop.c      |    1 +
 arch/x86/kernel/apic/apic_numachip.c  |    1 +
 arch/x86/kernel/apic/bigsmp_32.c      |    1 +
 arch/x86/kernel/apic/es7000_32.c      |    2 ++
 arch/x86/kernel/apic/numaq_32.c       |    1 +
 arch/x86/kernel/apic/probe_32.c       |    1 +
 arch/x86/kernel/apic/summit_32.c      |    1 +
 arch/x86/kernel/apic/x2apic_cluster.c |    1 +
 arch/x86/kernel/apic/x2apic_phys.c    |    1 +
 arch/x86/kernel/apic/x2apic_uv_x.c    |    1 +
 12 files changed, 27 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index a09e9ab..74efb8d 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -351,6 +351,13 @@ struct apic {
 	/* apic ops */
 	u32 (*read)(u32 reg);
 	void (*write)(u32 reg, u32 v);
+        /*
+	 * eoi_write has the same signature as write.
+	 * Drivers can support both eoi_write and write by passing the same
+	 * callback value. Kernel can override eoi_write and fall back
+	 * on write for EOI.
+	 */
+	void (*eoi_write)(u32 reg, u32 v);
 	u64 (*icr_read)(void);
 	void (*icr_write)(u32 low, u32 high);
 	void (*wait_icr_idle)(void);
@@ -426,6 +433,11 @@ static inline void apic_write(u32 reg, u32 val)
 	apic->write(reg, val);
 }
 
+static inline void apic_eoi(void)
+{
+	apic->eoi_write(APIC_EOI, APIC_EOI_ACK);
+}
+
 static inline u64 apic_icr_read(void)
 {
 	return apic->icr_read();
@@ -450,6 +462,7 @@ static inline u32 safe_apic_wait_icr_idle(void)
 
 static inline u32 apic_read(u32 reg) { return 0; }
 static inline void apic_write(u32 reg, u32 val) { }
+static inline void apic_eoi(void) { }
 static inline u64 apic_icr_read(void) { return 0; }
 static inline void apic_icr_write(u32 low, u32 high) { }
 static inline void apic_wait_icr_idle(void) { }
@@ -463,7 +476,7 @@ static inline void ack_APIC_irq(void)
 	 * ack_APIC_irq() actually gets compiled as a single instruction
 	 * ... yummie.
 	 */
-	apic_write(APIC_EOI, APIC_EOI_ACK);
+	apic_eoi();
 }
 
 static inline unsigned default_get_apic_id(unsigned long x)
diff --git a/arch/x86/kernel/apic/apic_flat_64.c b/arch/x86/kernel/apic/apic_flat_64.c
index 359b689..0e881c4 100644
--- a/arch/x86/kernel/apic/apic_flat_64.c
+++ b/arch/x86/kernel/apic/apic_flat_64.c
@@ -227,6 +227,7 @@ static struct apic apic_flat =  {
 
 	.read				= native_apic_mem_read,
 	.write				= native_apic_mem_write,
+	.eoi_write			= native_apic_mem_write,
 	.icr_read			= native_apic_icr_read,
 	.icr_write			= native_apic_icr_write,
 	.wait_icr_idle			= native_apic_wait_icr_idle,
@@ -386,6 +387,7 @@ static struct apic apic_physflat =  {
 
 	.read				= native_apic_mem_read,
 	.write				= native_apic_mem_write,
+	.eoi_write			= native_apic_mem_write,
 	.icr_read			= native_apic_icr_read,
 	.icr_write			= native_apic_icr_write,
 	.wait_icr_idle			= native_apic_wait_icr_idle,
diff --git a/arch/x86/kernel/apic/apic_noop.c b/arch/x86/kernel/apic/apic_noop.c
index 634ae6c..a6e4c6e 100644
--- a/arch/x86/kernel/apic/apic_noop.c
+++ b/arch/x86/kernel/apic/apic_noop.c
@@ -181,6 +181,7 @@ struct apic apic_noop = {
 
 	.read				= noop_apic_read,
 	.write				= noop_apic_write,
+	.eoi_write			= noop_apic_write,
 	.icr_read			= noop_apic_icr_read,
 	.icr_write			= noop_apic_icr_write,
 	.wait_icr_idle			= noop_apic_wait_icr_idle,
diff --git a/arch/x86/kernel/apic/apic_numachip.c b/arch/x86/kernel/apic/apic_numachip.c
index 23e7542..6ec6d5d 100644
--- a/arch/x86/kernel/apic/apic_numachip.c
+++ b/arch/x86/kernel/apic/apic_numachip.c
@@ -295,6 +295,7 @@ static struct apic apic_numachip __refconst = {
 
 	.read				= native_apic_mem_read,
 	.write				= native_apic_mem_write,
+	.eoi_write			= native_apic_mem_write,
 	.icr_read			= native_apic_icr_read,
 	.icr_write			= native_apic_icr_write,
 	.wait_icr_idle			= native_apic_wait_icr_idle,
diff --git a/arch/x86/kernel/apic/bigsmp_32.c b/arch/x86/kernel/apic/bigsmp_32.c
index 0cdec70..31fbdbf 100644
--- a/arch/x86/kernel/apic/bigsmp_32.c
+++ b/arch/x86/kernel/apic/bigsmp_32.c
@@ -248,6 +248,7 @@ static struct apic apic_bigsmp = {
 
 	.read				= native_apic_mem_read,
 	.write				= native_apic_mem_write,
+	.eoi_write			= native_apic_mem_write,
 	.icr_read			= native_apic_icr_read,
 	.icr_write			= native_apic_icr_write,
 	.wait_icr_idle			= native_apic_wait_icr_idle,
diff --git a/arch/x86/kernel/apic/es7000_32.c b/arch/x86/kernel/apic/es7000_32.c
index e42d1d3b9..db4ab1b 100644
--- a/arch/x86/kernel/apic/es7000_32.c
+++ b/arch/x86/kernel/apic/es7000_32.c
@@ -678,6 +678,7 @@ static struct apic __refdata apic_es7000_cluster = {
 
 	.read				= native_apic_mem_read,
 	.write				= native_apic_mem_write,
+	.eoi_write			= native_apic_mem_write,
 	.icr_read			= native_apic_icr_read,
 	.icr_write			= native_apic_icr_write,
 	.wait_icr_idle			= native_apic_wait_icr_idle,
@@ -742,6 +743,7 @@ static struct apic __refdata apic_es7000 = {
 
 	.read				= native_apic_mem_read,
 	.write				= native_apic_mem_write,
+	.eoi_write			= native_apic_mem_write,
 	.icr_read			= native_apic_icr_read,
 	.icr_write			= native_apic_icr_write,
 	.wait_icr_idle			= native_apic_wait_icr_idle,
diff --git a/arch/x86/kernel/apic/numaq_32.c b/arch/x86/kernel/apic/numaq_32.c
index 00d2422..f00a68c 100644
--- a/arch/x86/kernel/apic/numaq_32.c
+++ b/arch/x86/kernel/apic/numaq_32.c
@@ -530,6 +530,7 @@ static struct apic __refdata apic_numaq = {
 
 	.read				= native_apic_mem_read,
 	.write				= native_apic_mem_write,
+	.eoi_write			= native_apic_mem_write,
 	.icr_read			= native_apic_icr_read,
 	.icr_write			= native_apic_icr_write,
 	.wait_icr_idle			= native_apic_wait_icr_idle,
diff --git a/arch/x86/kernel/apic/probe_32.c b/arch/x86/kernel/apic/probe_32.c
index ff2c1b9..1b291da 100644
--- a/arch/x86/kernel/apic/probe_32.c
+++ b/arch/x86/kernel/apic/probe_32.c
@@ -142,6 +142,7 @@ static struct apic apic_default = {
 
 	.read				= native_apic_mem_read,
 	.write				= native_apic_mem_write,
+	.eoi_write			= native_apic_mem_write,
 	.icr_read			= native_apic_icr_read,
 	.icr_write			= native_apic_icr_write,
 	.wait_icr_idle			= native_apic_wait_icr_idle,
diff --git a/arch/x86/kernel/apic/summit_32.c b/arch/x86/kernel/apic/summit_32.c
index fea000b..659897c 100644
--- a/arch/x86/kernel/apic/summit_32.c
+++ b/arch/x86/kernel/apic/summit_32.c
@@ -546,6 +546,7 @@ static struct apic apic_summit = {
 
 	.read				= native_apic_mem_read,
 	.write				= native_apic_mem_write,
+	.eoi_write			= native_apic_mem_write,
 	.icr_read			= native_apic_icr_read,
 	.icr_write			= native_apic_icr_write,
 	.wait_icr_idle			= native_apic_wait_icr_idle,
diff --git a/arch/x86/kernel/apic/x2apic_cluster.c b/arch/x86/kernel/apic/x2apic_cluster.c
index 48f3103..a5baa78 100644
--- a/arch/x86/kernel/apic/x2apic_cluster.c
+++ b/arch/x86/kernel/apic/x2apic_cluster.c
@@ -260,6 +260,7 @@ static struct apic apic_x2apic_cluster = {
 
 	.read				= native_apic_msr_read,
 	.write				= native_apic_msr_write,
+	.eoi_write			= native_apic_msr_write,
 	.icr_read			= native_x2apic_icr_read,
 	.icr_write			= native_x2apic_icr_write,
 	.wait_icr_idle			= native_x2apic_wait_icr_idle,
diff --git a/arch/x86/kernel/apic/x2apic_phys.c b/arch/x86/kernel/apic/x2apic_phys.c
index 991e315..8340356 100644
--- a/arch/x86/kernel/apic/x2apic_phys.c
+++ b/arch/x86/kernel/apic/x2apic_phys.c
@@ -172,6 +172,7 @@ static struct apic apic_x2apic_phys = {
 
 	.read				= native_apic_msr_read,
 	.write				= native_apic_msr_write,
+	.eoi_write			= native_apic_msr_write,
 	.icr_read			= native_x2apic_icr_read,
 	.icr_write			= native_x2apic_icr_write,
 	.wait_icr_idle			= native_x2apic_wait_icr_idle,
diff --git a/arch/x86/kernel/apic/x2apic_uv_x.c b/arch/x86/kernel/apic/x2apic_uv_x.c
index 87bfa69..5b0e3d0 100644
--- a/arch/x86/kernel/apic/x2apic_uv_x.c
+++ b/arch/x86/kernel/apic/x2apic_uv_x.c
@@ -404,6 +404,7 @@ static struct apic __refdata apic_x2apic_uv_x = {
 
 	.read				= native_apic_msr_read,
 	.write				= native_apic_msr_write,
+	.eoi_write			= native_apic_msr_write,
 	.icr_read			= native_x2apic_icr_read,
 	.icr_write			= native_x2apic_icr_write,
 	.wait_icr_idle			= native_x2apic_wait_icr_idle,
-- 
MST

[PATCHv2 4/7] x86: eoi micro-optimization

[Michael S. Tsirkin]

We know both register and value for eoi beforehand,
so there's no need to check it and no need to do math
to calculate the msr. Saves instructions/branches
on each EOI when using x2apic.

I'm not sure what kind of tests should one run
to check whether this patch is good for performance.

Some data below: in case it's insufficient,
this patch can be dropped from the series for now:

I looked at the objdump output to verify that the generated code
looks right and actually is shorter.

Some benchmark results below show a tiny
but measureable improvement. The tests were run on
an AMD box with 24 cpus.

- A clean kernel build after reboot shows
a tiny but measureable improvement in system time
which means lower CPU overhead (though not measureable
in total time - that is dominated by user time and fluctuates
too much):

linux# reboot -f
...
linux# make clean
linux# time make -j 64 LOCALVERSION= 2>&1 > /dev/null

Before:

real    2m52.244s
user    35m53.833s
sys     6m7.194s

After:

real    2m52.827s
user    35m48.916s
sys     6m2.305s

- perf micro-benchmarks seem to consistently show
  a tiny improvement in total time as well but it's below
  the confidence level of 3 std deviations:

# ./tools/perf/perf   stat --sync --repeat 100 --null perf bench sched messaging
...
       0.414666797 seconds time elapsed ( +-  1.29% )

Performance counter stats for 'perf bench sched messaging' (100 runs):

       0.395370891 seconds time elapsed
( +-  1.04% )


# ./tools/perf/perf   stat --sync --repeat 100 --null perf bench sched pipe -l 10000
       0.307019664 seconds time elapsed
( +-  0.10% )

       0.304738024 seconds time elapsed
( +-  0.08% )


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 arch/x86/include/asm/apic.h           |    5 +++++
 arch/x86/kernel/apic/x2apic_cluster.c |    2 +-
 arch/x86/kernel/apic/x2apic_phys.c    |    2 +-
 arch/x86/kernel/apic/x2apic_uv_x.c    |    2 +-
 4 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index 74efb8d..5eb6d56 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -138,6 +138,11 @@ static inline void native_apic_msr_write(u32 reg, u32 v)
 	wrmsr(APIC_BASE_MSR + (reg >> 4), v, 0);
 }
 
+static inline void native_apic_msr_eoi_write(u32 reg, u32 v)
+{
+	wrmsr(APIC_BASE_MSR + (APIC_EOI >> 4), APIC_EOI_ACK, 0);
+}
+
 static inline u32 native_apic_msr_read(u32 reg)
 {
 	u64 msr;
diff --git a/arch/x86/kernel/apic/x2apic_cluster.c b/arch/x86/kernel/apic/x2apic_cluster.c
index a5baa78..ff35cff 100644
--- a/arch/x86/kernel/apic/x2apic_cluster.c
+++ b/arch/x86/kernel/apic/x2apic_cluster.c
@@ -260,7 +260,7 @@ static struct apic apic_x2apic_cluster = {
 
 	.read				= native_apic_msr_read,
 	.write				= native_apic_msr_write,
-	.eoi_write			= native_apic_msr_write,
+	.eoi_write			= native_apic_msr_eoi_write,
 	.icr_read			= native_x2apic_icr_read,
 	.icr_write			= native_x2apic_icr_write,
 	.wait_icr_idle			= native_x2apic_wait_icr_idle,
diff --git a/arch/x86/kernel/apic/x2apic_phys.c b/arch/x86/kernel/apic/x2apic_phys.c
index 8340356..c17e982 100644
--- a/arch/x86/kernel/apic/x2apic_phys.c
+++ b/arch/x86/kernel/apic/x2apic_phys.c
@@ -172,7 +172,7 @@ static struct apic apic_x2apic_phys = {
 
 	.read				= native_apic_msr_read,
 	.write				= native_apic_msr_write,
-	.eoi_write			= native_apic_msr_write,
+	.eoi_write			= native_apic_msr_eoi_write,
 	.icr_read			= native_x2apic_icr_read,
 	.icr_write			= native_x2apic_icr_write,
 	.wait_icr_idle			= native_x2apic_wait_icr_idle,
diff --git a/arch/x86/kernel/apic/x2apic_uv_x.c b/arch/x86/kernel/apic/x2apic_uv_x.c
index 5b0e3d0..c6d03f7 100644
--- a/arch/x86/kernel/apic/x2apic_uv_x.c
+++ b/arch/x86/kernel/apic/x2apic_uv_x.c
@@ -404,7 +404,7 @@ static struct apic __refdata apic_x2apic_uv_x = {
 
 	.read				= native_apic_msr_read,
 	.write				= native_apic_msr_write,
-	.eoi_write			= native_apic_msr_write,
+	.eoi_write			= native_apic_msr_eoi_write,
 	.icr_read			= native_x2apic_icr_read,
 	.icr_write			= native_x2apic_icr_write,
 	.wait_icr_idle			= native_x2apic_wait_icr_idle,
-- 
MST

[PATCHv2 5/7] kvm_para: guest side for eoi avoidance

[Michael S. Tsirkin]

The idea is simple: there's a bit, per APIC, in guest memory,
that tells the guest that it does not need EOI.
Guest tests it using a single est and clear operation - this is
necessary so that host can detect interrupt nesting - and if set, it can
skip the EOI MSR.

A simple microbenchmark shows exit reduction:

# perf stat -e 'kvm:*' -a sleep 1s

 Performance counter stats for 'sleep 1s':

            47,357 kvm:kvm_entry                                                [99.98%]
                 0 kvm:kvm_hypercall                                            [99.98%]
                 0 kvm:kvm_hv_hypercall                                         [99.98%]
             5,001 kvm:kvm_pio                                                  [99.98%]
                 0 kvm:kvm_cpuid                                                [99.98%]
            22,124 kvm:kvm_apic                                                 [99.98%]
            49,849 kvm:kvm_exit                                                 [99.98%]
            21,115 kvm:kvm_inj_virq                                             [99.98%]
                 0 kvm:kvm_inj_exception                                        [99.98%]
                 0 kvm:kvm_page_fault                                           [99.98%]
            22,937 kvm:kvm_msr                                                  [99.98%]
                 0 kvm:kvm_cr                                                   [99.98%]
                 0 kvm:kvm_pic_set_irq                                          [99.98%]
                 0 kvm:kvm_apic_ipi                                             [99.98%]
            22,207 kvm:kvm_apic_accept_irq                                      [99.98%]
            22,421 kvm:kvm_eoi                                                  [99.98%]
                 0 kvm:kvm_pv_eoi                                               [99.99%]
                 0 kvm:kvm_nested_vmrun                                         [99.99%]
                 0 kvm:kvm_nested_intercepts                                    [99.99%]
                 0 kvm:kvm_nested_vmexit                                        [99.99%]
                 0 kvm:kvm_nested_vmexit_inject                                    [99.99%]
                 0 kvm:kvm_nested_intr_vmexit                                    [99.99%]
                 0 kvm:kvm_invlpga                                              [99.99%]
                 0 kvm:kvm_skinit                                               [99.99%]
                57 kvm:kvm_emulate_insn                                         [99.99%]
                 0 kvm:vcpu_match_mmio                                          [99.99%]
                 0 kvm:kvm_userspace_exit                                       [99.99%]
                 2 kvm:kvm_set_irq                                              [99.99%]
                 2 kvm:kvm_ioapic_set_irq                                       [99.99%]
            23,609 kvm:kvm_msi_set_irq                                          [99.99%]
                 1 kvm:kvm_ack_irq                                              [99.99%]
               131 kvm:kvm_mmio                                                 [99.99%]
               226 kvm:kvm_fpu                                                  [100.00%]
                 0 kvm:kvm_age_page                                             [100.00%]
                 0 kvm:kvm_try_async_get_page                                    [100.00%]
                 0 kvm:kvm_async_pf_doublefault                                    [100.00%]
                 0 kvm:kvm_async_pf_not_present                                    [100.00%]
                 0 kvm:kvm_async_pf_ready                                       [100.00%]
                 0 kvm:kvm_async_pf_completed                                   

       1.002100578 seconds time elapsed

# perf stat -e 'kvm:*' -a sleep 1s

 Performance counter stats for 'sleep 1s':

            28,354 kvm:kvm_entry                                                [99.98%]
                 0 kvm:kvm_hypercall                                            [99.98%]
                 0 kvm:kvm_hv_hypercall                                         [99.98%]
             1,347 kvm:kvm_pio                                                  [99.98%]
                 0 kvm:kvm_cpuid                                                [99.98%]
             1,931 kvm:kvm_apic                                                 [99.98%]
            29,595 kvm:kvm_exit                                                 [99.98%]
            24,884 kvm:kvm_inj_virq                                             [99.98%]
                 0 kvm:kvm_inj_exception                                        [99.98%]
                 0 kvm:kvm_page_fault                                           [99.98%]
             1,986 kvm:kvm_msr                                                  [99.98%]
                 0 kvm:kvm_cr                                                   [99.98%]
                 0 kvm:kvm_pic_set_irq                                          [99.98%]
                 0 kvm:kvm_apic_ipi                                             [99.99%]
            25,953 kvm:kvm_apic_accept_irq                                      [99.99%]
            26,132 kvm:kvm_eoi                                                  [99.99%]
            26,593 kvm:kvm_pv_eoi                                               [99.99%]
                 0 kvm:kvm_nested_vmrun                                         [99.99%]
                 0 kvm:kvm_nested_intercepts                                    [99.99%]
                 0 kvm:kvm_nested_vmexit                                        [99.99%]
                 0 kvm:kvm_nested_vmexit_inject                                    [99.99%]
                 0 kvm:kvm_nested_intr_vmexit                                    [99.99%]
                 0 kvm:kvm_invlpga                                              [99.99%]
                 0 kvm:kvm_skinit                                               [99.99%]
               284 kvm:kvm_emulate_insn                                         [99.99%]
                68 kvm:vcpu_match_mmio                                          [99.99%]
                68 kvm:kvm_userspace_exit                                       [99.99%]
                 2 kvm:kvm_set_irq                                              [99.99%]
                 2 kvm:kvm_ioapic_set_irq                                       [99.99%]
            28,288 kvm:kvm_msi_set_irq                                          [99.99%]
                 1 kvm:kvm_ack_irq                                              [99.99%]
               131 kvm:kvm_mmio                                                 [100.00%]
               588 kvm:kvm_fpu                                                  [100.00%]
                 0 kvm:kvm_age_page                                             [100.00%]
                 0 kvm:kvm_try_async_get_page                                    [100.00%]
                 0 kvm:kvm_async_pf_doublefault                                    [100.00%]
                 0 kvm:kvm_async_pf_not_present                                    [100.00%]
                 0 kvm:kvm_async_pf_ready                                       [100.00%]
                 0 kvm:kvm_async_pf_completed                                   

       1.002039622 seconds time elapsed



Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 arch/x86/include/asm/bitops.h |    6 +++-
 arch/x86/kernel/kvm.c         |   50 ++++++++++++++++++++++++++++++++++++++--
 2 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index b97596e..c9c70ea 100644
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -26,11 +26,13 @@
 #if __GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 1)
 /* Technically wrong, but this avoids compilation errors on some gcc
    versions. */
-#define BITOP_ADDR(x) "=m" (*(volatile long *) (x))
+#define BITOP_ADDR_CONSTRAINT "=m"
 #else
-#define BITOP_ADDR(x) "+m" (*(volatile long *) (x))
+#define BITOP_ADDR_CONSTRAINT "+m"
 #endif
 
+#define BITOP_ADDR(x) BITOP_ADDR_CONSTRAINT (*(volatile long *) (x))
+
 #define ADDR				BITOP_ADDR(addr)
 
 /*
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index e554e5a..31f85cb 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -39,6 +39,8 @@
 #include <asm/desc.h>
 #include <asm/tlbflush.h>
 #include <asm/idle.h>
+#include <asm/apic.h>
+#include <asm/apicdef.h>
 
 static int kvmapf = 1;
 
@@ -283,6 +285,23 @@ static void kvm_register_steal_time(void)
 		cpu, __pa(st));
 }
 
+/* size alignment is implied but just to make it explicit. */
+static DEFINE_PER_CPU(unsigned long, kvm_apic_eoi) __aligned(2) = 0;
+
+static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
+{
+	/**
+	 * This relies on __test_and_clear_bit to modify the memory
+	 * in a way that is atomic with respect to the local CPU.
+	 * The hypervisor only accesses this memory from the local CPU so
+	 * there's no need for lock or memory barriers.
+	 * An optimization barrier is implied in apic write.
+	 */
+	if (__test_and_clear_bit(0, &__get_cpu_var(kvm_apic_eoi)))
+		return;
+	apic->write(APIC_EOI, APIC_EOI_ACK);
+}
+
 void __cpuinit kvm_guest_cpu_init(void)
 {
 	if (!kvm_para_available())
@@ -300,11 +319,17 @@ void __cpuinit kvm_guest_cpu_init(void)
 		       smp_processor_id());
 	}
 
+	if (kvm_para_has_feature(KVM_FEATURE_EOI)) {
+		__get_cpu_var(kvm_apic_eoi) = 0;
+		wrmsrl(MSR_KVM_EOI_EN, __pa(&__get_cpu_var(kvm_apic_eoi)) |
+		       KVM_MSR_ENABLED);
+	}
+
 	if (has_steal_clock)
 		kvm_register_steal_time();
 }
 
-static void kvm_pv_disable_apf(void *unused)
+static void kvm_pv_disable_apf(void)
 {
 	if (!__get_cpu_var(apf_reason).enabled)
 		return;
@@ -316,11 +341,18 @@ static void kvm_pv_disable_apf(void *unused)
 	       smp_processor_id());
 }
 
+static void kvm_pv_guest_cpu_reboot(void *unused)
+{
+	if (kvm_para_has_feature(KVM_FEATURE_EOI))
+		wrmsrl(MSR_KVM_EOI_EN, 0);
+	kvm_pv_disable_apf();
+}
+
 static int kvm_pv_reboot_notify(struct notifier_block *nb,
 				unsigned long code, void *unused)
 {
 	if (code == SYS_RESTART)
-		on_each_cpu(kvm_pv_disable_apf, NULL, 1);
+		on_each_cpu(kvm_pv_guest_cpu_reboot, NULL, 1);
 	return NOTIFY_DONE;
 }
 
@@ -371,7 +403,9 @@ static void __cpuinit kvm_guest_cpu_online(void *dummy)
 static void kvm_guest_cpu_offline(void *dummy)
 {
 	kvm_disable_steal_time();
-	kvm_pv_disable_apf(NULL);
+	if (kvm_para_has_feature(KVM_FEATURE_EOI))
+		wrmsrl(MSR_KVM_EOI_EN, 0);
+	kvm_pv_disable_apf();
 	apf_task_wake_all();
 }
 
@@ -424,6 +458,16 @@ void __init kvm_guest_init(void)
 		pv_time_ops.steal_clock = kvm_steal_clock;
 	}
 
+	if (kvm_para_has_feature(KVM_FEATURE_EOI)) {
+		struct apic **drv;
+
+		for (drv = __apicdrivers; drv < __apicdrivers_end; drv++) {
+			/* Should happen once for each apic */
+			WARN_ON((*drv)->eoi_write == kvm_guest_apic_eoi_write);
+			(*drv)->eoi_write = kvm_guest_apic_eoi_write;
+		}
+	}
+
 #ifdef CONFIG_SMP
 	smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
 	register_cpu_notifier(&kvm_cpu_notifier);
-- 
MST

[PATCHv2 6/7] x86/bitops: note on __test_and_clear_bit atomicity

[Michael S. Tsirkin]

__test_and_clear_bit is actually atomic with respect
to the local CPU. Add a note saying that KVM on x86
relies on this behaviour so people don't accidentaly break it.
Also warn not to rely on this in portable code.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 arch/x86/include/asm/bitops.h |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index c9c70ea..86f3a1e 100644
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -264,6 +264,13 @@ static inline int test_and_clear_bit(int nr, volatile unsigned long *addr)
  * This operation is non-atomic and can be reordered.
  * If two examples of this operation race, one can appear to succeed
  * but actually fail.  You must protect multiple accesses with a lock.
+ *
+ * Note: the operation is performed atomically with respect to
+ * the local CPU, but not other CPUs. Portable code should not
+ * rely on this behaviour.
+ * KVM relies on this behaviour on x86 for modifying memory that is also
+ * accessed from a hypervisor on the same CPU if running in a VM: don't change
+ * this without also updating arch/x86/kernel/kvm.c
  */
 static inline int __test_and_clear_bit(int nr, volatile unsigned long *addr)
 {
-- 
MST

[PATCHv2 7/7] kvm: host side for eoi optimization

[Michael S. Tsirkin]

Implementation of PV EOI using shared memory.
This reduces the number of exits an interrupt
causes as much as by half.

The idea is simple: there's a bit, per APIC, in guest memory,
that tells the guest that it does not need EOI.
We set it before injecting an interrupt and clear
before injecting a nested one. Guest tests it using
a test and clear operation - this is necessary
so that host can detect interrupt nesting -
and if set, it can skip the EOI MSR.

There's a new MSR to set the address of said register
in guest memory. Otherwise not much changed:
- Guest EOI is not required
- Register is tested & ISR is automatically cleared on exit

This patch is on top of kvm.git.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 arch/x86/include/asm/kvm_host.h |    6 ++
 arch/x86/include/asm/kvm_para.h |    2 +
 arch/x86/kvm/cpuid.c            |    1 +
 arch/x86/kvm/irq.c              |    2 +-
 arch/x86/kvm/lapic.c            |  109 +++++++++++++++++++++++++++++++++++++--
 arch/x86/kvm/lapic.h            |    2 +
 arch/x86/kvm/trace.h            |   34 ++++++++++++
 arch/x86/kvm/x86.c              |    8 +++-
 8 files changed, 157 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 32297f2..7673f4d 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -174,6 +174,7 @@ enum {
 
 /* apic attention bits */
 #define KVM_APIC_CHECK_VAPIC	0
+#define KVM_APIC_EOI_PENDING	1
 
 /*
  * We don't want allocation failures within the mmu code, so we preallocate
@@ -485,6 +486,11 @@ struct kvm_vcpu_arch {
 		u64 length;
 		u64 status;
 	} osvw;
+
+	struct {
+		u64 msr_val;
+		struct gfn_to_hva_cache data;
+	} eoi;
 };
 
 struct kvm_lpage_info {
diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index 734c376..195840d 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -22,6 +22,7 @@
 #define KVM_FEATURE_CLOCKSOURCE2        3
 #define KVM_FEATURE_ASYNC_PF		4
 #define KVM_FEATURE_STEAL_TIME		5
+#define KVM_FEATURE_EOI			6
 
 /* The last 8 bits are used to indicate how to interpret the flags field
  * in pvclock structure. If no bits are set, all flags are ignored.
@@ -37,6 +38,7 @@
 #define MSR_KVM_SYSTEM_TIME_NEW 0x4b564d01
 #define MSR_KVM_ASYNC_PF_EN 0x4b564d02
 #define MSR_KVM_STEAL_TIME  0x4b564d03
+#define MSR_KVM_EOI_EN      0x4b564d04
 
 struct kvm_steal_time {
 	__u64 steal;
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index eba8345..bda4877 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -408,6 +408,7 @@ static int do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 			     (1 << KVM_FEATURE_NOP_IO_DELAY) |
 			     (1 << KVM_FEATURE_CLOCKSOURCE2) |
 			     (1 << KVM_FEATURE_ASYNC_PF) |
+			     (1 << KVM_FEATURE_EOI) |
 			     (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
 
 		if (sched_info_on())
diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
index 7e06ba1..07bdfab 100644
--- a/arch/x86/kvm/irq.c
+++ b/arch/x86/kvm/irq.c
@@ -48,7 +48,7 @@ int kvm_cpu_has_interrupt(struct kvm_vcpu *v)
 	if (!irqchip_in_kernel(v->kvm))
 		return v->arch.interrupt.pending;
 
-	if (kvm_apic_has_interrupt(v) == -1) {	/* LAPIC */
+	if (kvm_apic_has_interrupt(v) < 0) {	/* LAPIC */
 		if (kvm_apic_accept_pic_intr(v)) {
 			s = pic_irqchip(v->kvm);	/* PIC */
 			return s->output;
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 93c1574..77e0244 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -270,6 +270,54 @@ int kvm_apic_set_irq(struct kvm_vcpu *vcpu, struct kvm_lapic_irq *irq)
 			irq->level, irq->trig_mode);
 }
 
+static int eoi_put_user(struct kvm_vcpu *vcpu, u8 val)
+{
+
+	return kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.eoi.data, &val,
+				      sizeof(val));
+}
+
+static int eoi_get_user(struct kvm_vcpu *vcpu, u8 *val)
+{
+
+	return kvm_read_guest_cached(vcpu->kvm, &vcpu->arch.eoi.data, val,
+				      sizeof(*val));
+}
+
+static inline bool eoi_enabled(struct kvm_vcpu *vcpu)
+{
+	return vcpu->arch.eoi.msr_val & KVM_MSR_ENABLED;
+}
+
+static bool eoi_get_pending(struct kvm_vcpu *vcpu)
+{
+	u8 val;
+	if (eoi_get_user(vcpu, &val) < 0)
+		apic_debug("Can't read EOI MSR value: 0x%llx\n",
+			   (unsigned long long)vcpi->arch.eoi.msr_val);
+	return val & 0x1;
+}
+
+static void eoi_set_pending(struct kvm_vcpu *vcpu)
+{
+	if (eoi_put_user(vcpu, 0x1) < 0) {
+		apic_debug("Can't set EOI MSR value: 0x%llx\n",
+			   (unsigned long long)vcpi->arch.eoi.msr_val);
+		return;
+	}
+	__set_bit(KVM_APIC_EOI_PENDING, &vcpu->arch.apic_attention);
+}
+
+static void eoi_clr_pending(struct kvm_vcpu *vcpu)
+{
+	if (eoi_put_user(vcpu, 0x0) < 0) {
+		apic_debug("Can't clear EOI MSR value: 0x%llx\n",
+			   (unsigned long long)vcpi->arch.eoi.msr_val);
+		return;
+	}
+	__clear_bit(KVM_APIC_EOI_PENDING, &vcpu->arch.apic_attention);
+}
+
 static inline int apic_find_highest_isr(struct kvm_lapic *apic)
 {
 	int result;
@@ -482,16 +530,21 @@ int kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2)
 	return vcpu1->arch.apic_arb_prio - vcpu2->arch.apic_arb_prio;
 }
 
-static void apic_set_eoi(struct kvm_lapic *apic)
+static int apic_set_eoi(struct kvm_lapic *apic)
 {
 	int vector = apic_find_highest_isr(apic);
+
+	trace_kvm_eoi(apic, vector);
+
 	/*
 	 * Not every write EOI will has corresponding ISR,
 	 * one example is when Kernel check timer on setup_IO_APIC
 	 */
 	if (vector == -1)
-		return;
+		return vector;
 
+	if (eoi_enabled(apic->vcpu))
+		eoi_clr_pending(apic->vcpu);
 	apic_clear_vector(vector, apic->regs + APIC_ISR);
 	apic_update_ppr(apic);
 
@@ -505,6 +558,7 @@ static void apic_set_eoi(struct kvm_lapic *apic)
 		kvm_ioapic_update_eoi(apic->vcpu->kvm, vector, trigger_mode);
 	}
 	kvm_make_request(KVM_REQ_EVENT, apic->vcpu);
+	return vector;
 }
 
 static void apic_send_ipi(struct kvm_lapic *apic)
@@ -1085,6 +1139,7 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu)
 	atomic_set(&apic->lapic_timer.pending, 0);
 	if (kvm_vcpu_is_bsp(vcpu))
 		vcpu->arch.apic_base |= MSR_IA32_APICBASE_BSP;
+	vcpu->arch.eoi.msr_val = 0;
 	apic_update_ppr(apic);
 
 	vcpu->arch.apic_arb_prio = 0;
@@ -1211,9 +1266,10 @@ int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu)
 
 	apic_update_ppr(apic);
 	highest_irr = apic_find_highest_irr(apic);
-	if ((highest_irr == -1) ||
-	    ((highest_irr & 0xF0) <= apic_get_reg(apic, APIC_PROCPRI)))
+	if (highest_irr == -1)
 		return -1;
+	if (((highest_irr & 0xF0) <= apic_get_reg(apic, APIC_PROCPRI)))
+		return -2;
 	return highest_irr;
 }
 
@@ -1245,9 +1301,20 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
 	int vector = kvm_apic_has_interrupt(vcpu);
 	struct kvm_lapic *apic = vcpu->arch.apic;
 
-	if (vector == -1)
+	/* Detect interrupt nesting and disable EOI optimization */
+	if (eoi_enabled(vcpu) && vector == -2)
+		eoi_clr_pending(vcpu);
+
+	if (vector < 0)
 		return -1;
 
+	if (eoi_enabled(vcpu)) {
+		if (kvm_ioapic_handles_vector(vcpu->kvm, vector))
+			eoi_clr_pending(vcpu);
+		else
+			eoi_set_pending(vcpu);
+	}
+
 	apic_set_vector(vector, apic->regs + APIC_ISR);
 	apic_update_ppr(apic);
 	apic_clear_irr(vector, apic);
@@ -1262,6 +1329,14 @@ void kvm_apic_post_state_restore(struct kvm_vcpu *vcpu)
 			     MSR_IA32_APICBASE_BASE;
 	kvm_apic_set_version(vcpu);
 
+	if (eoi_enabled(apic->vcpu)) {
+		if (eoi_get_pending(apic->vcpu))
+			__set_bit(KVM_APIC_EOI_PENDING,
+				  &vcpu->arch.apic_attention);
+		else
+			__clear_bit(KVM_APIC_EOI_PENDING,
+				    &vcpu->arch.apic_attention);
+	}
 	apic_update_ppr(apic);
 	hrtimer_cancel(&apic->lapic_timer.timer);
 	update_divide_count(apic);
@@ -1283,11 +1358,25 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
 		hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
 }
 
+static void apic_update_eoi(struct kvm_lapic *apic)
+{
+	int vector;
+	BUG_ON(!eoi_enabled(apic->vcpu));
+	if (eoi_get_pending(apic->vcpu))
+		return;
+	__clear_bit(KVM_APIC_EOI_PENDING, &apic->vcpu->arch.apic_attention);
+	vector = apic_set_eoi(apic);
+	trace_kvm_pv_eoi(apic, vector);
+}
+
 void kvm_lapic_sync_from_vapic(struct kvm_vcpu *vcpu)
 {
 	u32 data;
 	void *vapic;
 
+	if (test_bit(KVM_APIC_EOI_PENDING, &vcpu->arch.apic_attention))
+		apic_update_eoi(vcpu->arch.apic);
+
 	if (!test_bit(KVM_APIC_CHECK_VAPIC, &vcpu->arch.apic_attention))
 		return;
 
@@ -1394,3 +1483,13 @@ int kvm_hv_vapic_msr_read(struct kvm_vcpu *vcpu, u32 reg, u64 *data)
 
 	return 0;
 }
+
+int kvm_pv_enable_apic_eoi(struct kvm_vcpu *vcpu, u64 data)
+{
+	u64 addr = data & ~KVM_MSR_ENABLED;
+	if (eoi_enabled(vcpu))
+		eoi_clr_pending(vcpu);
+	vcpu->arch.eoi.msr_val = data;
+	kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.eoi.data, addr);
+	return 0;
+}
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 6f4ce25..042dace 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -60,4 +60,6 @@ static inline bool kvm_hv_vapic_assist_page_enabled(struct kvm_vcpu *vcpu)
 {
 	return vcpu->arch.hv_vapic & HV_X64_MSR_APIC_ASSIST_PAGE_ENABLE;
 }
+
+int kvm_pv_enable_apic_eoi(struct kvm_vcpu *vcpu, u64 data);
 #endif
diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
index 911d264..851914e 100644
--- a/arch/x86/kvm/trace.h
+++ b/arch/x86/kvm/trace.h
@@ -517,6 +517,40 @@ TRACE_EVENT(kvm_apic_accept_irq,
 		  __entry->coalesced ? " (coalesced)" : "")
 );
 
+TRACE_EVENT(kvm_eoi,
+	    TP_PROTO(struct kvm_lapic *apic, int vector),
+	    TP_ARGS(apic, vector),
+
+	TP_STRUCT__entry(
+		__field(	__u32,		apicid		)
+		__field(	int,		vector		)
+	),
+
+	TP_fast_assign(
+		__entry->apicid		= apic->vcpu->vcpu_id;
+		__entry->vector		= vector;
+	),
+
+	TP_printk("apicid %x vector %d", __entry->apicid, __entry->vector)
+);
+
+TRACE_EVENT(kvm_pv_eoi,
+	    TP_PROTO(struct kvm_lapic *apic, int vector),
+	    TP_ARGS(apic, vector),
+
+	TP_STRUCT__entry(
+		__field(	__u32,		apicid		)
+		__field(	int,		vector		)
+	),
+
+	TP_fast_assign(
+		__entry->apicid		= apic->vcpu->vcpu_id;
+		__entry->vector		= vector;
+	),
+
+	TP_printk("apicid %x vector %d", __entry->apicid, __entry->vector)
+);
+
 /*
  * Tracepoint for nested VMRUN
  */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 185a2b8..bfcd97d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -795,6 +795,7 @@ static u32 msrs_to_save[] = {
 	MSR_KVM_SYSTEM_TIME_NEW, MSR_KVM_WALL_CLOCK_NEW,
 	HV_X64_MSR_GUEST_OS_ID, HV_X64_MSR_HYPERCALL,
 	HV_X64_MSR_APIC_ASSIST_PAGE, MSR_KVM_ASYNC_PF_EN, MSR_KVM_STEAL_TIME,
+	MSR_KVM_EOI_EN,
 	MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
 	MSR_STAR,
 #ifdef CONFIG_X86_64
@@ -1653,6 +1654,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 		kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
 
 		break;
+	case MSR_KVM_EOI_EN:
+		if (kvm_pv_enable_apic_eoi(vcpu, data))
+			return 1;
+		break;
 
 	case MSR_IA32_MCG_CTL:
 	case MSR_IA32_MCG_STATUS:
@@ -5370,7 +5375,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	if (unlikely(vcpu->arch.tsc_always_catchup))
 		kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
 
-	kvm_lapic_sync_from_vapic(vcpu);
+	if (unlikely(vcpu->arch.apic_attention))
+		kvm_lapic_sync_from_vapic(vcpu);
 
 	r = kvm_x86_ops->handle_exit(vcpu);
 out:
-- 
MST

Re: [PATCHv2 7/7] kvm: host side for eoi optimization

[Gleb Natapov]

On Fri, May 11, 2012 at 10:38:40AM +0300, Michael S. Tsirkin wrote:
> Implementation of PV EOI using shared memory.
> This reduces the number of exits an interrupt
> causes as much as by half.
> 
> The idea is simple: there's a bit, per APIC, in guest memory,
> that tells the guest that it does not need EOI.
> We set it before injecting an interrupt and clear
> before injecting a nested one. Guest tests it using
> a test and clear operation - this is necessary
> so that host can detect interrupt nesting -
> and if set, it can skip the EOI MSR.
> 
> There's a new MSR to set the address of said register
> in guest memory. Otherwise not much changed:
> - Guest EOI is not required
> - Register is tested & ISR is automatically cleared on exit
> 
> This patch is on top of kvm.git.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  arch/x86/include/asm/kvm_host.h |    6 ++
>  arch/x86/include/asm/kvm_para.h |    2 +
>  arch/x86/kvm/cpuid.c            |    1 +
>  arch/x86/kvm/irq.c              |    2 +-
>  arch/x86/kvm/lapic.c            |  109 +++++++++++++++++++++++++++++++++++++--
>  arch/x86/kvm/lapic.h            |    2 +
>  arch/x86/kvm/trace.h            |   34 ++++++++++++
>  arch/x86/kvm/x86.c              |    8 +++-
Documentation ++++++ :)

>  8 files changed, 157 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 32297f2..7673f4d 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -174,6 +174,7 @@ enum {
>  
>  /* apic attention bits */
>  #define KVM_APIC_CHECK_VAPIC	0
> +#define KVM_APIC_EOI_PENDING	1
>  
>  /*
>   * We don't want allocation failures within the mmu code, so we preallocate
> @@ -485,6 +486,11 @@ struct kvm_vcpu_arch {
>  		u64 length;
>  		u64 status;
>  	} osvw;
> +
> +	struct {
> +		u64 msr_val;
> +		struct gfn_to_hva_cache data;
> +	} eoi;
>  };
>  
>  struct kvm_lpage_info {
> diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> index 734c376..195840d 100644
> --- a/arch/x86/include/asm/kvm_para.h
> +++ b/arch/x86/include/asm/kvm_para.h
> @@ -22,6 +22,7 @@
>  #define KVM_FEATURE_CLOCKSOURCE2        3
>  #define KVM_FEATURE_ASYNC_PF		4
>  #define KVM_FEATURE_STEAL_TIME		5
> +#define KVM_FEATURE_EOI			6
>  
>  /* The last 8 bits are used to indicate how to interpret the flags field
>   * in pvclock structure. If no bits are set, all flags are ignored.
> @@ -37,6 +38,7 @@
>  #define MSR_KVM_SYSTEM_TIME_NEW 0x4b564d01
>  #define MSR_KVM_ASYNC_PF_EN 0x4b564d02
>  #define MSR_KVM_STEAL_TIME  0x4b564d03
> +#define MSR_KVM_EOI_EN      0x4b564d04
>  
>  struct kvm_steal_time {
>  	__u64 steal;
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index eba8345..bda4877 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -408,6 +408,7 @@ static int do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  			     (1 << KVM_FEATURE_NOP_IO_DELAY) |
>  			     (1 << KVM_FEATURE_CLOCKSOURCE2) |
>  			     (1 << KVM_FEATURE_ASYNC_PF) |
> +			     (1 << KVM_FEATURE_EOI) |
>  			     (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
>  
>  		if (sched_info_on())
> diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
> index 7e06ba1..07bdfab 100644
> --- a/arch/x86/kvm/irq.c
> +++ b/arch/x86/kvm/irq.c
> @@ -48,7 +48,7 @@ int kvm_cpu_has_interrupt(struct kvm_vcpu *v)
>  	if (!irqchip_in_kernel(v->kvm))
>  		return v->arch.interrupt.pending;
>  
> -	if (kvm_apic_has_interrupt(v) == -1) {	/* LAPIC */
> +	if (kvm_apic_has_interrupt(v) < 0) {	/* LAPIC */
>  		if (kvm_apic_accept_pic_intr(v)) {
>  			s = pic_irqchip(v->kvm);	/* PIC */
>  			return s->output;
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 93c1574..77e0244 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -270,6 +270,54 @@ int kvm_apic_set_irq(struct kvm_vcpu *vcpu, struct kvm_lapic_irq *irq)
>  			irq->level, irq->trig_mode);
>  }
>  
> +static int eoi_put_user(struct kvm_vcpu *vcpu, u8 val)
> +{
> +
> +	return kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.eoi.data, &val,
> +				      sizeof(val));
> +}
> +
> +static int eoi_get_user(struct kvm_vcpu *vcpu, u8 *val)
> +{
> +
> +	return kvm_read_guest_cached(vcpu->kvm, &vcpu->arch.eoi.data, val,
> +				      sizeof(*val));
> +}
> +
> +static inline bool eoi_enabled(struct kvm_vcpu *vcpu)
> +{
> +	return vcpu->arch.eoi.msr_val & KVM_MSR_ENABLED;
> +}
> +
> +static bool eoi_get_pending(struct kvm_vcpu *vcpu)
> +{
> +	u8 val;
> +	if (eoi_get_user(vcpu, &val) < 0)
> +		apic_debug("Can't read EOI MSR value: 0x%llx\n",
> +			   (unsigned long long)vcpi->arch.eoi.msr_val);
> +	return val & 0x1;
> +}
> +
> +static void eoi_set_pending(struct kvm_vcpu *vcpu)
> +{
> +	if (eoi_put_user(vcpu, 0x1) < 0) {
> +		apic_debug("Can't set EOI MSR value: 0x%llx\n",
> +			   (unsigned long long)vcpi->arch.eoi.msr_val);
> +		return;
> +	}
> +	__set_bit(KVM_APIC_EOI_PENDING, &vcpu->arch.apic_attention);
> +}
> +
> +static void eoi_clr_pending(struct kvm_vcpu *vcpu)
> +{
> +	if (eoi_put_user(vcpu, 0x0) < 0) {
> +		apic_debug("Can't clear EOI MSR value: 0x%llx\n",
> +			   (unsigned long long)vcpi->arch.eoi.msr_val);
> +		return;
> +	}
> +	__clear_bit(KVM_APIC_EOI_PENDING, &vcpu->arch.apic_attention);
> +}
> +
>  static inline int apic_find_highest_isr(struct kvm_lapic *apic)
>  {
>  	int result;
> @@ -482,16 +530,21 @@ int kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2)
>  	return vcpu1->arch.apic_arb_prio - vcpu2->arch.apic_arb_prio;
>  }
>  
> -static void apic_set_eoi(struct kvm_lapic *apic)
> +static int apic_set_eoi(struct kvm_lapic *apic)
>  {
>  	int vector = apic_find_highest_isr(apic);
> +
> +	trace_kvm_eoi(apic, vector);
> +
>  	/*
>  	 * Not every write EOI will has corresponding ISR,
>  	 * one example is when Kernel check timer on setup_IO_APIC
>  	 */
>  	if (vector == -1)
> -		return;
> +		return vector;
>  
> +	if (eoi_enabled(apic->vcpu))
> +		eoi_clr_pending(apic->vcpu);
>  	apic_clear_vector(vector, apic->regs + APIC_ISR);
>  	apic_update_ppr(apic);
>  
> @@ -505,6 +558,7 @@ static void apic_set_eoi(struct kvm_lapic *apic)
>  		kvm_ioapic_update_eoi(apic->vcpu->kvm, vector, trigger_mode);
>  	}
>  	kvm_make_request(KVM_REQ_EVENT, apic->vcpu);
> +	return vector;
>  }
>  
>  static void apic_send_ipi(struct kvm_lapic *apic)
> @@ -1085,6 +1139,7 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu)
>  	atomic_set(&apic->lapic_timer.pending, 0);
>  	if (kvm_vcpu_is_bsp(vcpu))
>  		vcpu->arch.apic_base |= MSR_IA32_APICBASE_BSP;
> +	vcpu->arch.eoi.msr_val = 0;
>  	apic_update_ppr(apic);
>  
>  	vcpu->arch.apic_arb_prio = 0;
> @@ -1211,9 +1266,10 @@ int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu)
>  
>  	apic_update_ppr(apic);
>  	highest_irr = apic_find_highest_irr(apic);
> -	if ((highest_irr == -1) ||
> -	    ((highest_irr & 0xF0) <= apic_get_reg(apic, APIC_PROCPRI)))
> +	if (highest_irr == -1)
>  		return -1;
> +	if (((highest_irr & 0xF0) <= apic_get_reg(apic, APIC_PROCPRI)))
> +		return -2;
>  	return highest_irr;
>  }
>  
> @@ -1245,9 +1301,20 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
>  	int vector = kvm_apic_has_interrupt(vcpu);
>  	struct kvm_lapic *apic = vcpu->arch.apic;
>  
> -	if (vector == -1)
> +	/* Detect interrupt nesting and disable EOI optimization */
> +	if (eoi_enabled(vcpu) && vector == -2)
> +		eoi_clr_pending(vcpu);
> +
> +	if (vector < 0)
>  		return -1;
>  
> +	if (eoi_enabled(vcpu)) {
> +		if (kvm_ioapic_handles_vector(vcpu->kvm, vector))
> +			eoi_clr_pending(vcpu);
> +		else
> +			eoi_set_pending(vcpu);
> +	}
> +
>  	apic_set_vector(vector, apic->regs + APIC_ISR);
>  	apic_update_ppr(apic);
>  	apic_clear_irr(vector, apic);
> @@ -1262,6 +1329,14 @@ void kvm_apic_post_state_restore(struct kvm_vcpu *vcpu)
>  			     MSR_IA32_APICBASE_BASE;
>  	kvm_apic_set_version(vcpu);
>  
> +	if (eoi_enabled(apic->vcpu)) {
> +		if (eoi_get_pending(apic->vcpu))
> +			__set_bit(KVM_APIC_EOI_PENDING,
> +				  &vcpu->arch.apic_attention);
> +		else
> +			__clear_bit(KVM_APIC_EOI_PENDING,
> +				    &vcpu->arch.apic_attention);
> +	}
>  	apic_update_ppr(apic);
>  	hrtimer_cancel(&apic->lapic_timer.timer);
>  	update_divide_count(apic);
> @@ -1283,11 +1358,25 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
>  		hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
>  }
>  
> +static void apic_update_eoi(struct kvm_lapic *apic)
> +{
> +	int vector;
> +	BUG_ON(!eoi_enabled(apic->vcpu));
> +	if (eoi_get_pending(apic->vcpu))
> +		return;
> +	__clear_bit(KVM_APIC_EOI_PENDING, &apic->vcpu->arch.apic_attention);
> +	vector = apic_set_eoi(apic);
> +	trace_kvm_pv_eoi(apic, vector);
> +}
> +
>  void kvm_lapic_sync_from_vapic(struct kvm_vcpu *vcpu)
>  {
>  	u32 data;
>  	void *vapic;
>  
> +	if (test_bit(KVM_APIC_EOI_PENDING, &vcpu->arch.apic_attention))
> +		apic_update_eoi(vcpu->arch.apic);
> +
>  	if (!test_bit(KVM_APIC_CHECK_VAPIC, &vcpu->arch.apic_attention))
>  		return;
>  
> @@ -1394,3 +1483,13 @@ int kvm_hv_vapic_msr_read(struct kvm_vcpu *vcpu, u32 reg, u64 *data)
>  
>  	return 0;
>  }
> +
> +int kvm_pv_enable_apic_eoi(struct kvm_vcpu *vcpu, u64 data)
> +{
> +	u64 addr = data & ~KVM_MSR_ENABLED;
Since documentation is missing I do not know what alignment addr should
have, but if it is more than 2 bytes we should check if reserved bits
are not zero and #GP if they are.

> +	if (eoi_enabled(vcpu))
> +		eoi_clr_pending(vcpu);
> +	vcpu->arch.eoi.msr_val = data;
> +	kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.eoi.data, addr);
This may fail.

> +	return 0;
> +}
> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> index 6f4ce25..042dace 100644
> --- a/arch/x86/kvm/lapic.h
> +++ b/arch/x86/kvm/lapic.h
> @@ -60,4 +60,6 @@ static inline bool kvm_hv_vapic_assist_page_enabled(struct kvm_vcpu *vcpu)
>  {
>  	return vcpu->arch.hv_vapic & HV_X64_MSR_APIC_ASSIST_PAGE_ENABLE;
>  }
> +
> +int kvm_pv_enable_apic_eoi(struct kvm_vcpu *vcpu, u64 data);
>  #endif
> diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
> index 911d264..851914e 100644
> --- a/arch/x86/kvm/trace.h
> +++ b/arch/x86/kvm/trace.h
> @@ -517,6 +517,40 @@ TRACE_EVENT(kvm_apic_accept_irq,
>  		  __entry->coalesced ? " (coalesced)" : "")
>  );
>  
> +TRACE_EVENT(kvm_eoi,
> +	    TP_PROTO(struct kvm_lapic *apic, int vector),
> +	    TP_ARGS(apic, vector),
> +
> +	TP_STRUCT__entry(
> +		__field(	__u32,		apicid		)
> +		__field(	int,		vector		)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->apicid		= apic->vcpu->vcpu_id;
> +		__entry->vector		= vector;
> +	),
> +
> +	TP_printk("apicid %x vector %d", __entry->apicid, __entry->vector)
> +);
> +
> +TRACE_EVENT(kvm_pv_eoi,
> +	    TP_PROTO(struct kvm_lapic *apic, int vector),
> +	    TP_ARGS(apic, vector),
> +
> +	TP_STRUCT__entry(
> +		__field(	__u32,		apicid		)
> +		__field(	int,		vector		)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->apicid		= apic->vcpu->vcpu_id;
> +		__entry->vector		= vector;
> +	),
> +
> +	TP_printk("apicid %x vector %d", __entry->apicid, __entry->vector)
> +);
> +
>  /*
>   * Tracepoint for nested VMRUN
>   */
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 185a2b8..bfcd97d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -795,6 +795,7 @@ static u32 msrs_to_save[] = {
>  	MSR_KVM_SYSTEM_TIME_NEW, MSR_KVM_WALL_CLOCK_NEW,
>  	HV_X64_MSR_GUEST_OS_ID, HV_X64_MSR_HYPERCALL,
>  	HV_X64_MSR_APIC_ASSIST_PAGE, MSR_KVM_ASYNC_PF_EN, MSR_KVM_STEAL_TIME,
> +	MSR_KVM_EOI_EN,
>  	MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
>  	MSR_STAR,
>  #ifdef CONFIG_X86_64
> @@ -1653,6 +1654,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
>  		kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
>  
>  		break;
> +	case MSR_KVM_EOI_EN:
> +		if (kvm_pv_enable_apic_eoi(vcpu, data))
> +			return 1;
> +		break;
>  
>  	case MSR_IA32_MCG_CTL:
>  	case MSR_IA32_MCG_STATUS:
> @@ -5370,7 +5375,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  	if (unlikely(vcpu->arch.tsc_always_catchup))
>  		kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
>  
> -	kvm_lapic_sync_from_vapic(vcpu);
> +	if (unlikely(vcpu->arch.apic_attention))
> +		kvm_lapic_sync_from_vapic(vcpu);
>  
>  	r = kvm_x86_ops->handle_exit(vcpu);
>  out:
> -- 
> MST

--
			Gleb.

Re: [PATCHv2 7/7] kvm: host side for eoi optimization

[Michael S. Tsirkin]

On Sun, May 13, 2012 at 12:33:17PM +0300, Gleb Natapov wrote:
> On Fri, May 11, 2012 at 10:38:40AM +0300, Michael S. Tsirkin wrote:
> > Implementation of PV EOI using shared memory.
> > This reduces the number of exits an interrupt
> > causes as much as by half.
> > 
> > The idea is simple: there's a bit, per APIC, in guest memory,
> > that tells the guest that it does not need EOI.
> > We set it before injecting an interrupt and clear
> > before injecting a nested one. Guest tests it using
> > a test and clear operation - this is necessary
> > so that host can detect interrupt nesting -
> > and if set, it can skip the EOI MSR.
> > 
> > There's a new MSR to set the address of said register
> > in guest memory. Otherwise not much changed:
> > - Guest EOI is not required
> > - Register is tested & ISR is automatically cleared on exit
> > 
> > This patch is on top of kvm.git.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >  arch/x86/include/asm/kvm_host.h |    6 ++
> >  arch/x86/include/asm/kvm_para.h |    2 +
> >  arch/x86/kvm/cpuid.c            |    1 +
> >  arch/x86/kvm/irq.c              |    2 +-
> >  arch/x86/kvm/lapic.c            |  109 +++++++++++++++++++++++++++++++++++++--
> >  arch/x86/kvm/lapic.h            |    2 +
> >  arch/x86/kvm/trace.h            |   34 ++++++++++++
> >  arch/x86/kvm/x86.c              |    8 +++-
> Documentation ++++++ :)

Right. Will do. Documentation/virtual/kvm/msr.txt
is probably enough?

> >  8 files changed, 157 insertions(+), 7 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 32297f2..7673f4d 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -174,6 +174,7 @@ enum {
> >  
> >  /* apic attention bits */
> >  #define KVM_APIC_CHECK_VAPIC	0
> > +#define KVM_APIC_EOI_PENDING	1
> >  
> >  /*
> >   * We don't want allocation failures within the mmu code, so we preallocate
> > @@ -485,6 +486,11 @@ struct kvm_vcpu_arch {
> >  		u64 length;
> >  		u64 status;
> >  	} osvw;
> > +
> > +	struct {
> > +		u64 msr_val;
> > +		struct gfn_to_hva_cache data;
> > +	} eoi;
> >  };
> >  
> >  struct kvm_lpage_info {
> > diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> > index 734c376..195840d 100644
> > --- a/arch/x86/include/asm/kvm_para.h
> > +++ b/arch/x86/include/asm/kvm_para.h
> > @@ -22,6 +22,7 @@
> >  #define KVM_FEATURE_CLOCKSOURCE2        3
> >  #define KVM_FEATURE_ASYNC_PF		4
> >  #define KVM_FEATURE_STEAL_TIME		5
> > +#define KVM_FEATURE_EOI			6
> >  
> >  /* The last 8 bits are used to indicate how to interpret the flags field
> >   * in pvclock structure. If no bits are set, all flags are ignored.
> > @@ -37,6 +38,7 @@
> >  #define MSR_KVM_SYSTEM_TIME_NEW 0x4b564d01
> >  #define MSR_KVM_ASYNC_PF_EN 0x4b564d02
> >  #define MSR_KVM_STEAL_TIME  0x4b564d03
> > +#define MSR_KVM_EOI_EN      0x4b564d04
> >  
> >  struct kvm_steal_time {
> >  	__u64 steal;
> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > index eba8345..bda4877 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -408,6 +408,7 @@ static int do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
> >  			     (1 << KVM_FEATURE_NOP_IO_DELAY) |
> >  			     (1 << KVM_FEATURE_CLOCKSOURCE2) |
> >  			     (1 << KVM_FEATURE_ASYNC_PF) |
> > +			     (1 << KVM_FEATURE_EOI) |
> >  			     (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
> >  
> >  		if (sched_info_on())
> > diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
> > index 7e06ba1..07bdfab 100644
> > --- a/arch/x86/kvm/irq.c
> > +++ b/arch/x86/kvm/irq.c
> > @@ -48,7 +48,7 @@ int kvm_cpu_has_interrupt(struct kvm_vcpu *v)
> >  	if (!irqchip_in_kernel(v->kvm))
> >  		return v->arch.interrupt.pending;
> >  
> > -	if (kvm_apic_has_interrupt(v) == -1) {	/* LAPIC */
> > +	if (kvm_apic_has_interrupt(v) < 0) {	/* LAPIC */
> >  		if (kvm_apic_accept_pic_intr(v)) {
> >  			s = pic_irqchip(v->kvm);	/* PIC */
> >  			return s->output;
> > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > index 93c1574..77e0244 100644
> > --- a/arch/x86/kvm/lapic.c
> > +++ b/arch/x86/kvm/lapic.c
> > @@ -270,6 +270,54 @@ int kvm_apic_set_irq(struct kvm_vcpu *vcpu, struct kvm_lapic_irq *irq)
> >  			irq->level, irq->trig_mode);
> >  }
> >  
> > +static int eoi_put_user(struct kvm_vcpu *vcpu, u8 val)
> > +{
> > +
> > +	return kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.eoi.data, &val,
> > +				      sizeof(val));
> > +}
> > +
> > +static int eoi_get_user(struct kvm_vcpu *vcpu, u8 *val)
> > +{
> > +
> > +	return kvm_read_guest_cached(vcpu->kvm, &vcpu->arch.eoi.data, val,
> > +				      sizeof(*val));
> > +}
> > +
> > +static inline bool eoi_enabled(struct kvm_vcpu *vcpu)
> > +{
> > +	return vcpu->arch.eoi.msr_val & KVM_MSR_ENABLED;
> > +}
> > +
> > +static bool eoi_get_pending(struct kvm_vcpu *vcpu)
> > +{
> > +	u8 val;
> > +	if (eoi_get_user(vcpu, &val) < 0)
> > +		apic_debug("Can't read EOI MSR value: 0x%llx\n",
> > +			   (unsigned long long)vcpi->arch.eoi.msr_val);
> > +	return val & 0x1;
> > +}
> > +
> > +static void eoi_set_pending(struct kvm_vcpu *vcpu)
> > +{
> > +	if (eoi_put_user(vcpu, 0x1) < 0) {
> > +		apic_debug("Can't set EOI MSR value: 0x%llx\n",
> > +			   (unsigned long long)vcpi->arch.eoi.msr_val);
> > +		return;
> > +	}
> > +	__set_bit(KVM_APIC_EOI_PENDING, &vcpu->arch.apic_attention);
> > +}
> > +
> > +static void eoi_clr_pending(struct kvm_vcpu *vcpu)
> > +{
> > +	if (eoi_put_user(vcpu, 0x0) < 0) {
> > +		apic_debug("Can't clear EOI MSR value: 0x%llx\n",
> > +			   (unsigned long long)vcpi->arch.eoi.msr_val);
> > +		return;
> > +	}
> > +	__clear_bit(KVM_APIC_EOI_PENDING, &vcpu->arch.apic_attention);
> > +}
> > +
> >  static inline int apic_find_highest_isr(struct kvm_lapic *apic)
> >  {
> >  	int result;
> > @@ -482,16 +530,21 @@ int kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2)
> >  	return vcpu1->arch.apic_arb_prio - vcpu2->arch.apic_arb_prio;
> >  }
> >  
> > -static void apic_set_eoi(struct kvm_lapic *apic)
> > +static int apic_set_eoi(struct kvm_lapic *apic)
> >  {
> >  	int vector = apic_find_highest_isr(apic);
> > +
> > +	trace_kvm_eoi(apic, vector);
> > +
> >  	/*
> >  	 * Not every write EOI will has corresponding ISR,
> >  	 * one example is when Kernel check timer on setup_IO_APIC
> >  	 */
> >  	if (vector == -1)
> > -		return;
> > +		return vector;
> >  
> > +	if (eoi_enabled(apic->vcpu))
> > +		eoi_clr_pending(apic->vcpu);
> >  	apic_clear_vector(vector, apic->regs + APIC_ISR);
> >  	apic_update_ppr(apic);
> >  
> > @@ -505,6 +558,7 @@ static void apic_set_eoi(struct kvm_lapic *apic)
> >  		kvm_ioapic_update_eoi(apic->vcpu->kvm, vector, trigger_mode);
> >  	}
> >  	kvm_make_request(KVM_REQ_EVENT, apic->vcpu);
> > +	return vector;
> >  }
> >  
> >  static void apic_send_ipi(struct kvm_lapic *apic)
> > @@ -1085,6 +1139,7 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu)
> >  	atomic_set(&apic->lapic_timer.pending, 0);
> >  	if (kvm_vcpu_is_bsp(vcpu))
> >  		vcpu->arch.apic_base |= MSR_IA32_APICBASE_BSP;
> > +	vcpu->arch.eoi.msr_val = 0;
> >  	apic_update_ppr(apic);
> >  
> >  	vcpu->arch.apic_arb_prio = 0;
> > @@ -1211,9 +1266,10 @@ int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu)
> >  
> >  	apic_update_ppr(apic);
> >  	highest_irr = apic_find_highest_irr(apic);
> > -	if ((highest_irr == -1) ||
> > -	    ((highest_irr & 0xF0) <= apic_get_reg(apic, APIC_PROCPRI)))
> > +	if (highest_irr == -1)
> >  		return -1;
> > +	if (((highest_irr & 0xF0) <= apic_get_reg(apic, APIC_PROCPRI)))
> > +		return -2;
> >  	return highest_irr;
> >  }
> >  
> > @@ -1245,9 +1301,20 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
> >  	int vector = kvm_apic_has_interrupt(vcpu);
> >  	struct kvm_lapic *apic = vcpu->arch.apic;
> >  
> > -	if (vector == -1)
> > +	/* Detect interrupt nesting and disable EOI optimization */
> > +	if (eoi_enabled(vcpu) && vector == -2)
> > +		eoi_clr_pending(vcpu);
> > +
> > +	if (vector < 0)
> >  		return -1;
> >  
> > +	if (eoi_enabled(vcpu)) {
> > +		if (kvm_ioapic_handles_vector(vcpu->kvm, vector))
> > +			eoi_clr_pending(vcpu);
> > +		else
> > +			eoi_set_pending(vcpu);
> > +	}
> > +
> >  	apic_set_vector(vector, apic->regs + APIC_ISR);
> >  	apic_update_ppr(apic);
> >  	apic_clear_irr(vector, apic);
> > @@ -1262,6 +1329,14 @@ void kvm_apic_post_state_restore(struct kvm_vcpu *vcpu)
> >  			     MSR_IA32_APICBASE_BASE;
> >  	kvm_apic_set_version(vcpu);
> >  
> > +	if (eoi_enabled(apic->vcpu)) {
> > +		if (eoi_get_pending(apic->vcpu))
> > +			__set_bit(KVM_APIC_EOI_PENDING,
> > +				  &vcpu->arch.apic_attention);
> > +		else
> > +			__clear_bit(KVM_APIC_EOI_PENDING,
> > +				    &vcpu->arch.apic_attention);
> > +	}
> >  	apic_update_ppr(apic);
> >  	hrtimer_cancel(&apic->lapic_timer.timer);
> >  	update_divide_count(apic);
> > @@ -1283,11 +1358,25 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
> >  		hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
> >  }
> >  
> > +static void apic_update_eoi(struct kvm_lapic *apic)
> > +{
> > +	int vector;
> > +	BUG_ON(!eoi_enabled(apic->vcpu));
> > +	if (eoi_get_pending(apic->vcpu))
> > +		return;
> > +	__clear_bit(KVM_APIC_EOI_PENDING, &apic->vcpu->arch.apic_attention);
> > +	vector = apic_set_eoi(apic);
> > +	trace_kvm_pv_eoi(apic, vector);
> > +}
> > +
> >  void kvm_lapic_sync_from_vapic(struct kvm_vcpu *vcpu)
> >  {
> >  	u32 data;
> >  	void *vapic;
> >  
> > +	if (test_bit(KVM_APIC_EOI_PENDING, &vcpu->arch.apic_attention))
> > +		apic_update_eoi(vcpu->arch.apic);
> > +
> >  	if (!test_bit(KVM_APIC_CHECK_VAPIC, &vcpu->arch.apic_attention))
> >  		return;
> >  
> > @@ -1394,3 +1483,13 @@ int kvm_hv_vapic_msr_read(struct kvm_vcpu *vcpu, u32 reg, u64 *data)
> >  
> >  	return 0;
> >  }
> > +
> > +int kvm_pv_enable_apic_eoi(struct kvm_vcpu *vcpu, u64 data)
> > +{
> > +	u64 addr = data & ~KVM_MSR_ENABLED;
> Since documentation is missing I do not know what alignment addr should
> have, but if it is more than 2 bytes we should check if reserved bits
> are not zero and #GP if they are.

Two bytes are required.

> > +	if (eoi_enabled(vcpu))
> > +		eoi_clr_pending(vcpu);
> > +	vcpu->arch.eoi.msr_val = data;
> > +	kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.eoi.data, addr);
> This may fail.

On invalid address, yes. Then the cache hva will be set to invalid
so accesses will fail too. So a malicious guest is only hurting
itself.
Maybe add a comment here?

> > +	return 0;
> > +}
> > diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> > index 6f4ce25..042dace 100644
> > --- a/arch/x86/kvm/lapic.h
> > +++ b/arch/x86/kvm/lapic.h
> > @@ -60,4 +60,6 @@ static inline bool kvm_hv_vapic_assist_page_enabled(struct kvm_vcpu *vcpu)
> >  {
> >  	return vcpu->arch.hv_vapic & HV_X64_MSR_APIC_ASSIST_PAGE_ENABLE;
> >  }
> > +
> > +int kvm_pv_enable_apic_eoi(struct kvm_vcpu *vcpu, u64 data);
> >  #endif
> > diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
> > index 911d264..851914e 100644
> > --- a/arch/x86/kvm/trace.h
> > +++ b/arch/x86/kvm/trace.h
> > @@ -517,6 +517,40 @@ TRACE_EVENT(kvm_apic_accept_irq,
> >  		  __entry->coalesced ? " (coalesced)" : "")
> >  );
> >  
> > +TRACE_EVENT(kvm_eoi,
> > +	    TP_PROTO(struct kvm_lapic *apic, int vector),
> > +	    TP_ARGS(apic, vector),
> > +
> > +	TP_STRUCT__entry(
> > +		__field(	__u32,		apicid		)
> > +		__field(	int,		vector		)
> > +	),
> > +
> > +	TP_fast_assign(
> > +		__entry->apicid		= apic->vcpu->vcpu_id;
> > +		__entry->vector		= vector;
> > +	),
> > +
> > +	TP_printk("apicid %x vector %d", __entry->apicid, __entry->vector)
> > +);
> > +
> > +TRACE_EVENT(kvm_pv_eoi,
> > +	    TP_PROTO(struct kvm_lapic *apic, int vector),
> > +	    TP_ARGS(apic, vector),
> > +
> > +	TP_STRUCT__entry(
> > +		__field(	__u32,		apicid		)
> > +		__field(	int,		vector		)
> > +	),
> > +
> > +	TP_fast_assign(
> > +		__entry->apicid		= apic->vcpu->vcpu_id;
> > +		__entry->vector		= vector;
> > +	),
> > +
> > +	TP_printk("apicid %x vector %d", __entry->apicid, __entry->vector)
> > +);
> > +
> >  /*
> >   * Tracepoint for nested VMRUN
> >   */
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 185a2b8..bfcd97d 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -795,6 +795,7 @@ static u32 msrs_to_save[] = {
> >  	MSR_KVM_SYSTEM_TIME_NEW, MSR_KVM_WALL_CLOCK_NEW,
> >  	HV_X64_MSR_GUEST_OS_ID, HV_X64_MSR_HYPERCALL,
> >  	HV_X64_MSR_APIC_ASSIST_PAGE, MSR_KVM_ASYNC_PF_EN, MSR_KVM_STEAL_TIME,
> > +	MSR_KVM_EOI_EN,
> >  	MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
> >  	MSR_STAR,
> >  #ifdef CONFIG_X86_64
> > @@ -1653,6 +1654,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
> >  		kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
> >  
> >  		break;
> > +	case MSR_KVM_EOI_EN:
> > +		if (kvm_pv_enable_apic_eoi(vcpu, data))
> > +			return 1;
> > +		break;
> >  
> >  	case MSR_IA32_MCG_CTL:
> >  	case MSR_IA32_MCG_STATUS:
> > @@ -5370,7 +5375,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> >  	if (unlikely(vcpu->arch.tsc_always_catchup))
> >  		kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
> >  
> > -	kvm_lapic_sync_from_vapic(vcpu);
> > +	if (unlikely(vcpu->arch.apic_attention))
> > +		kvm_lapic_sync_from_vapic(vcpu);
> >  
> >  	r = kvm_x86_ops->handle_exit(vcpu);
> >  out:
> > -- 
> > MST
> 
> --
> 			Gleb.

Re: [PATCHv2 7/7] kvm: host side for eoi optimization

[Gleb Natapov]

On Sun, May 13, 2012 at 01:01:28PM +0300, Michael S. Tsirkin wrote:
> > > +	if (eoi_enabled(vcpu))
> > > +		eoi_clr_pending(vcpu);
> > > +	vcpu->arch.eoi.msr_val = data;
> > > +	kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.eoi.data, addr);
> > This may fail.
> 
> On invalid address, yes. Then the cache hva will be set to invalid
> so accesses will fail too. So a malicious guest is only hurting
> itself.
> Maybe add a comment here?
> 
Kill it with #GP like other MSRs do.

--
			Gleb.

Re: [PATCHv2 7/7] kvm: host side for eoi optimization

[Michael S. Tsirkin]

On Sun, May 13, 2012 at 12:33:17PM +0300, Gleb Natapov wrote:
> >  arch/x86/include/asm/kvm_host.h |    6 ++
> >  arch/x86/include/asm/kvm_para.h |    2 +
> >  arch/x86/kvm/cpuid.c            |    1 +
> >  arch/x86/kvm/irq.c              |    2 +-
> >  arch/x86/kvm/lapic.c            |  109 +++++++++++++++++++++++++++++++++++++--
> >  arch/x86/kvm/lapic.h            |    2 +
> >  arch/x86/kvm/trace.h            |   34 ++++++++++++
> >  arch/x86/kvm/x86.c              |    8 +++-
> Documentation ++++++ :)

I just sent out some documentation. Didn't want to
repost the whole patchset to acoid spamming the list,
I hope you and others can use it for review.

Thanks,
MST

[PATCH] qemu: whitelist kvm pv eoi feature

[Michael S. Tsirkin]

Whitelist kvm pv eoi feature. The feature is enabled
with -cpu kvm64. To disable: -cpu kvm64,-kvm_eoi.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---

Sending a copy to kernel list as this is needed
to test the pv eoi feature recently submitted.

 target-i386/cpuid.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/target-i386/cpuid.c b/target-i386/cpuid.c
index 465ea15..c421b19 100644
--- a/target-i386/cpuid.c
+++ b/target-i386/cpuid.c
@@ -75,7 +75,7 @@ static const char *ext3_feature_name[] = {
 };
 
 static const char *kvm_feature_name[] = {
-    "kvmclock", "kvm_nopiodelay", "kvm_mmu", "kvmclock", "kvm_asyncpf", NULL, NULL, NULL,
+    "kvmclock", "kvm_nopiodelay", "kvm_mmu", "kvmclock", "kvm_asyncpf", NULL, "kvm_eoi", NULL,
     NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
     NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
     NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
-- 
MST

[Qemu-devel] [PATCH] qemu: whitelist kvm pv eoi feature

[Michael S. Tsirkin]

Whitelist kvm pv eoi feature. The feature is enabled
with -cpu kvm64. To disable: -cpu kvm64,-kvm_eoi.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---

Sending a copy to kernel list as this is needed
to test the pv eoi feature recently submitted.

 target-i386/cpuid.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/target-i386/cpuid.c b/target-i386/cpuid.c
index 465ea15..c421b19 100644
--- a/target-i386/cpuid.c
+++ b/target-i386/cpuid.c
@@ -75,7 +75,7 @@ static const char *ext3_feature_name[] = {
 };
 
 static const char *kvm_feature_name[] = {
-    "kvmclock", "kvm_nopiodelay", "kvm_mmu", "kvmclock", "kvm_asyncpf", NULL, NULL, NULL,
+    "kvmclock", "kvm_nopiodelay", "kvm_mmu", "kvmclock", "kvm_asyncpf", NULL, "kvm_eoi", NULL,
     NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
     NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
     NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
-- 
MST

[PATCH] qemu: whitelist kvm pv eoi feature

[Michael S. Tsirkin]

Whitelist kvm pv eoi feature. The feature is enabled
with -cpu kvm64. To disable: -cpu kvm64,-kvm_eoi.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---

Sending a copy to kernel list as this is needed
to test the pv eoi feature recently submitted.

 target-i386/cpuid.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/target-i386/cpuid.c b/target-i386/cpuid.c
index 465ea15..c421b19 100644
--- a/target-i386/cpuid.c
+++ b/target-i386/cpuid.c
@@ -75,7 +75,7 @@ static const char *ext3_feature_name[] = {
 };
 
 static const char *kvm_feature_name[] = {
-    "kvmclock", "kvm_nopiodelay", "kvm_mmu", "kvmclock", "kvm_asyncpf", NULL, NULL, NULL,
+    "kvmclock", "kvm_nopiodelay", "kvm_mmu", "kvmclock", "kvm_asyncpf", NULL, "kvm_eoi", NULL,
     NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
     NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
     NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
-- 
MST

Re: [Qemu-devel] [PATCH] qemu: whitelist kvm pv eoi feature

[Eric Blake]

[-- Attachment #1: Type: text/plain, Size: 1152 bytes --]

[adding libvirt, dropping kernel]

On 05/11/2012 01:43 AM, Michael S. Tsirkin wrote:
> Whitelist kvm pv eoi feature. The feature is enabled
> with -cpu kvm64. To disable: -cpu kvm64,-kvm_eoi.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> 
> Sending a copy to kernel list as this is needed
> to test the pv eoi feature recently submitted.
> 
>  target-i386/cpuid.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/target-i386/cpuid.c b/target-i386/cpuid.c
> index 465ea15..c421b19 100644
> --- a/target-i386/cpuid.c
> +++ b/target-i386/cpuid.c
> @@ -75,7 +75,7 @@ static const char *ext3_feature_name[] = {
>  };
>  
>  static const char *kvm_feature_name[] = {
> -    "kvmclock", "kvm_nopiodelay", "kvm_mmu", "kvmclock", "kvm_asyncpf", NULL, NULL, NULL,
> +    "kvmclock", "kvm_nopiodelay", "kvm_mmu", "kvmclock", "kvm_asyncpf", NULL, "kvm_eoi", NULL,

Should libvirt also be recognizing this processor capability in its XML
in order to drive the -kvm_eoi option?

-- 
Eric Blake   eblake@redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: [Qemu-devel] [PATCH] qemu: whitelist kvm pv eoi feature

[Michael S. Tsirkin]

On Fri, May 11, 2012 at 06:47:43AM -0600, Eric Blake wrote:
> [adding libvirt, dropping kernel]
> 
> On 05/11/2012 01:43 AM, Michael S. Tsirkin wrote:
> > Whitelist kvm pv eoi feature. The feature is enabled
> > with -cpu kvm64. To disable: -cpu kvm64,-kvm_eoi.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> > 
> > Sending a copy to kernel list as this is needed
> > to test the pv eoi feature recently submitted.
> > 
> >  target-i386/cpuid.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/target-i386/cpuid.c b/target-i386/cpuid.c
> > index 465ea15..c421b19 100644
> > --- a/target-i386/cpuid.c
> > +++ b/target-i386/cpuid.c
> > @@ -75,7 +75,7 @@ static const char *ext3_feature_name[] = {
> >  };
> >  
> >  static const char *kvm_feature_name[] = {
> > -    "kvmclock", "kvm_nopiodelay", "kvm_mmu", "kvmclock", "kvm_asyncpf", NULL, NULL, NULL,
> > +    "kvmclock", "kvm_nopiodelay", "kvm_mmu", "kvmclock", "kvm_asyncpf", NULL, "kvm_eoi", NULL,
> 
> Should libvirt also be recognizing this processor capability in its XML
> in order to drive the -kvm_eoi option?

I think so.

> -- 
> Eric Blake   eblake@redhat.com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
> 

Re: [PATCH] qemu: whitelist kvm pv eoi feature

[Michael S. Tsirkin]

On Sun, May 13, 2012 at 03:02:58PM +0300, Michael S. Tsirkin wrote:
> On Fri, May 11, 2012 at 06:47:43AM -0600, Eric Blake wrote:
> > [adding libvirt, dropping kernel]
> > 
> > On 05/11/2012 01:43 AM, Michael S. Tsirkin wrote:
> > > Whitelist kvm pv eoi feature. The feature is enabled
> > > with -cpu kvm64. To disable: -cpu kvm64,-kvm_eoi.
> > > 
> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > ---
> > > 
> > > Sending a copy to kernel list as this is needed
> > > to test the pv eoi feature recently submitted.
> > > 
> > >  target-i386/cpuid.c |    2 +-
> > >  1 files changed, 1 insertions(+), 1 deletions(-)
> > > 
> > > diff --git a/target-i386/cpuid.c b/target-i386/cpuid.c
> > > index 465ea15..c421b19 100644
> > > --- a/target-i386/cpuid.c
> > > +++ b/target-i386/cpuid.c
> > > @@ -75,7 +75,7 @@ static const char *ext3_feature_name[] = {
> > >  };
> > >  
> > >  static const char *kvm_feature_name[] = {
> > > -    "kvmclock", "kvm_nopiodelay", "kvm_mmu", "kvmclock", "kvm_asyncpf", NULL, NULL, NULL,
> > > +    "kvmclock", "kvm_nopiodelay", "kvm_mmu", "kvmclock", "kvm_asyncpf", NULL, "kvm_eoi", NULL,
> > 
> > Should libvirt also be recognizing this processor capability in its XML
> > in order to drive the -kvm_eoi option?
> 
> I think so.

A follow-up question: does libvirt use -cpu kvm?
How are such features normally handled for
cross-version migration?

> > -- 
> > Eric Blake   eblake@redhat.com    +1-919-301-3266
> > Libvirt virtualization library http://libvirt.org
> > 
> 
> 

Re: [Qemu-devel] [PATCH] qemu: whitelist kvm pv eoi feature

[Michael S. Tsirkin]

On Sun, May 13, 2012 at 03:02:58PM +0300, Michael S. Tsirkin wrote:
> On Fri, May 11, 2012 at 06:47:43AM -0600, Eric Blake wrote:
> > [adding libvirt, dropping kernel]
> > 
> > On 05/11/2012 01:43 AM, Michael S. Tsirkin wrote:
> > > Whitelist kvm pv eoi feature. The feature is enabled
> > > with -cpu kvm64. To disable: -cpu kvm64,-kvm_eoi.
> > > 
> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > ---
> > > 
> > > Sending a copy to kernel list as this is needed
> > > to test the pv eoi feature recently submitted.
> > > 
> > >  target-i386/cpuid.c |    2 +-
> > >  1 files changed, 1 insertions(+), 1 deletions(-)
> > > 
> > > diff --git a/target-i386/cpuid.c b/target-i386/cpuid.c
> > > index 465ea15..c421b19 100644
> > > --- a/target-i386/cpuid.c
> > > +++ b/target-i386/cpuid.c
> > > @@ -75,7 +75,7 @@ static const char *ext3_feature_name[] = {
> > >  };
> > >  
> > >  static const char *kvm_feature_name[] = {
> > > -    "kvmclock", "kvm_nopiodelay", "kvm_mmu", "kvmclock", "kvm_asyncpf", NULL, NULL, NULL,
> > > +    "kvmclock", "kvm_nopiodelay", "kvm_mmu", "kvmclock", "kvm_asyncpf", NULL, "kvm_eoi", NULL,
> > 
> > Should libvirt also be recognizing this processor capability in its XML
> > in order to drive the -kvm_eoi option?
> 
> I think so.

A follow-up question: does libvirt use -cpu kvm?
How are such features normally handled for
cross-version migration?

> > -- 
> > Eric Blake   eblake@redhat.com    +1-919-301-3266
> > Libvirt virtualization library http://libvirt.org
> > 
> 
>