[PATCH] x86/hvm: Remove callback from paging->flush_tlb() hook

Andrew Cooper posted 1 patch 2 weeks, 4 days ago
Failed in applying to current master (apply log)
xen/arch/x86/hvm/hvm.c               |  7 +------
xen/arch/x86/hvm/viridian/viridian.c | 31 +++++++++----------------------
xen/arch/x86/mm/hap/hap.c            | 11 ++++++++---
xen/arch/x86/mm/shadow/common.c      | 18 +++++++++++-------
xen/arch/x86/mm/shadow/private.h     |  3 +--
xen/include/asm-x86/paging.h         | 11 ++++-------
6 files changed, 34 insertions(+), 47 deletions(-)

[PATCH] x86/hvm: Remove callback from paging->flush_tlb() hook

Posted by Andrew Cooper 2 weeks, 4 days ago
TLB flushing is a hotpath, and function pointer calls are
expensive (especially under repoline) for what amounts to an identity
transform on the data.  Just pass the vcpu_bitmap bitmap directly.

As we use NULL for all rather than none, introduce a flush_vcpu() helper to
avoid the risk of logical errors from opencoding the expression.  This also
means the viridian callers can avoid writing an all-ones bitmap for the
flushing logic to consume.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Wei Liu <wl@xen.org>
CC: Paul Durrant <paul@xen.org>

The result even compiles smaller:

  $ ../scripts/bloat-o-meter xen-syms-before xen-syms-after
  add/remove: 0/2 grow/shrink: 0/3 up/down: 0/-125 (-125)
  Function                                     old     new   delta
  flush_tlb                                    207     205      -2
  always_flush                                   6       -      -6
  need_flush                                     9       -      -9
  do_hvm_op                                   2434    2418     -16
  shadow_flush_tlb                             628     536     -92

but this is very much not the point of the patch.

It would be rather more efficient in this case and probably others for
for_each_vcpu() to iterate over d->vcpu[] than follow the v->next_vcpu pointer
chain (better locality of access), and also because then the vCPU id is the
loop induction variable, not a value read from memory.
---
 xen/arch/x86/hvm/hvm.c               |  7 +------
 xen/arch/x86/hvm/viridian/viridian.c | 31 +++++++++----------------------
 xen/arch/x86/mm/hap/hap.c            | 11 ++++++++---
 xen/arch/x86/mm/shadow/common.c      | 18 +++++++++++-------
 xen/arch/x86/mm/shadow/private.h     |  3 +--
 xen/include/asm-x86/paging.h         | 11 ++++-------
 6 files changed, 34 insertions(+), 47 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index eee365711d63..31e9474db093 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4047,17 +4047,12 @@ static void hvm_s3_resume(struct domain *d)
     }
 }
 
-static bool always_flush(void *ctxt, struct vcpu *v)
-{
-    return true;
-}
-
 static int hvmop_flush_tlb_all(void)
 {
     if ( !is_hvm_domain(current->domain) )
         return -EINVAL;
 
-    return paging_flush_tlb(always_flush, NULL) ? 0 : -ERESTART;
+    return paging_flush_tlb(NULL) ? 0 : -ERESTART;
 }
 
 static int hvmop_set_evtchn_upcall_vector(
diff --git a/xen/arch/x86/hvm/viridian/viridian.c b/xen/arch/x86/hvm/viridian/viridian.c
index b906f7b86a74..cab0bbee5cde 100644
--- a/xen/arch/x86/hvm/viridian/viridian.c
+++ b/xen/arch/x86/hvm/viridian/viridian.c
@@ -574,13 +574,6 @@ static void vpmask_fill(struct hypercall_vpmask *vpmask)
     bitmap_fill(vpmask->mask, HVM_MAX_VCPUS);
 }
 
-static bool vpmask_test(const struct hypercall_vpmask *vpmask,
-                        unsigned int vp)
-{
-    ASSERT(vp < HVM_MAX_VCPUS);
-    return test_bit(vp, vpmask->mask);
-}
-
 static unsigned int vpmask_first(const struct hypercall_vpmask *vpmask)
 {
     return find_first_bit(vpmask->mask, HVM_MAX_VCPUS);
@@ -669,17 +662,6 @@ static uint16_t hv_vpset_to_vpmask(const struct hv_vpset *set,
 #undef NR_VPS_PER_BANK
 }
 
-/*
- * Windows should not issue the hypercalls requiring this callback in the
- * case where vcpu_id would exceed the size of the mask.
- */
-static bool need_flush(void *ctxt, struct vcpu *v)
-{
-    struct hypercall_vpmask *vpmask = ctxt;
-
-    return vpmask_test(vpmask, v->vcpu_id);
-}
-
 union hypercall_input {
     uint64_t raw;
     struct {
@@ -714,6 +696,7 @@ static int hvcall_flush(const union hypercall_input *input,
         uint64_t flags;
         uint64_t vcpu_mask;
     } input_params;
+    unsigned long *vcpu_bitmap;
 
     /* These hypercalls should never use the fast-call convention. */
     if ( input->fast )
@@ -730,18 +713,19 @@ static int hvcall_flush(const union hypercall_input *input,
      * so err on the safe side.
      */
     if ( input_params.flags & HV_FLUSH_ALL_PROCESSORS )
-        vpmask_fill(vpmask);
+        vcpu_bitmap = NULL;
     else
     {
         vpmask_empty(vpmask);
         vpmask_set(vpmask, 0, input_params.vcpu_mask);
+        vcpu_bitmap = vpmask->mask;
     }
 
     /*
      * A false return means that another vcpu is currently trying
      * a similar operation, so back off.
      */
-    if ( !paging_flush_tlb(need_flush, vpmask) )
+    if ( !paging_flush_tlb(vcpu_bitmap) )
         return -ERESTART;
 
     output->rep_complete = input->rep_count;
@@ -760,6 +744,7 @@ static int hvcall_flush_ex(const union hypercall_input *input,
         uint64_t flags;
         struct hv_vpset set;
     } input_params;
+    unsigned long *vcpu_bitmap;
 
     /* These hypercalls should never use the fast-call convention. */
     if ( input->fast )
@@ -771,7 +756,7 @@ static int hvcall_flush_ex(const union hypercall_input *input,
         return -EINVAL;
 
     if ( input_params.flags & HV_FLUSH_ALL_PROCESSORS )
-        vpmask_fill(vpmask);
+        vcpu_bitmap = NULL;
     else
     {
         union hypercall_vpset *vpset = &this_cpu(hypercall_vpset);
@@ -807,13 +792,15 @@ static int hvcall_flush_ex(const union hypercall_input *input,
         rc = hv_vpset_to_vpmask(set, vpmask);
         if ( rc )
             return rc;
+
+        vcpu_bitmap = vpmask->mask;
     }
 
     /*
      * A false return means that another vcpu is currently trying
      * a similar operation, so back off.
      */
-    if ( !paging_flush_tlb(need_flush, vpmask) )
+    if ( !paging_flush_tlb(vcpu_bitmap) )
         return -ERESTART;
 
     output->rep_complete = input->rep_count;
diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
index 73575deb0d8a..84d7a1b7906a 100644
--- a/xen/arch/x86/mm/hap/hap.c
+++ b/xen/arch/x86/mm/hap/hap.c
@@ -705,8 +705,13 @@ static void dummy_flush(void *data)
 {
 }
 
-static bool flush_tlb(bool (*flush_vcpu)(void *ctxt, struct vcpu *v),
-                      void *ctxt)
+static bool flush_vcpu(const struct vcpu *v, const unsigned long *vcpu_bitmap)
+{
+    return !vcpu_bitmap || test_bit(v->vcpu_id, vcpu_bitmap);
+}
+
+/* Flush TLB of selected vCPUs.  NULL for all. */
+static bool flush_tlb(const unsigned long *vcpu_bitmap)
 {
     static DEFINE_PER_CPU(cpumask_t, flush_cpumask);
     cpumask_t *mask = &this_cpu(flush_cpumask);
@@ -721,7 +726,7 @@ static bool flush_tlb(bool (*flush_vcpu)(void *ctxt, struct vcpu *v),
     {
         unsigned int cpu;
 
-        if ( !flush_vcpu(ctxt, v) )
+        if ( !flush_vcpu(v, vcpu_bitmap) )
             continue;
 
         hvm_asid_flush_vcpu(v);
diff --git a/xen/arch/x86/mm/shadow/common.c b/xen/arch/x86/mm/shadow/common.c
index 8c1b041f7135..de09ef5cae58 100644
--- a/xen/arch/x86/mm/shadow/common.c
+++ b/xen/arch/x86/mm/shadow/common.c
@@ -3069,9 +3069,13 @@ static void sh_clean_dirty_bitmap(struct domain *d)
 }
 
 
-/* Fluhs TLB of selected vCPUs. */
-bool shadow_flush_tlb(bool (*flush_vcpu)(void *ctxt, struct vcpu *v),
-                      void *ctxt)
+static bool flush_vcpu(const struct vcpu *v, const unsigned long *vcpu_bitmap)
+{
+    return !vcpu_bitmap || test_bit(v->vcpu_id, vcpu_bitmap);
+}
+
+/* Flush TLB of selected vCPUs.  NULL for all. */
+bool shadow_flush_tlb(const unsigned long *vcpu_bitmap)
 {
     static DEFINE_PER_CPU(cpumask_t, flush_cpumask);
     cpumask_t *mask = &this_cpu(flush_cpumask);
@@ -3084,12 +3088,12 @@ bool shadow_flush_tlb(bool (*flush_vcpu)(void *ctxt, struct vcpu *v),
 
     /* Pause all other vcpus. */
     for_each_vcpu ( d, v )
-        if ( v != current && flush_vcpu(ctxt, v) )
+        if ( v != current && flush_vcpu(v, vcpu_bitmap) )
             vcpu_pause_nosync(v);
 
     /* Now that all VCPUs are signalled to deschedule, we wait... */
     for_each_vcpu ( d, v )
-        if ( v != current && flush_vcpu(ctxt, v) )
+        if ( v != current && flush_vcpu(v, vcpu_bitmap) )
             while ( !vcpu_runnable(v) && v->is_running )
                 cpu_relax();
 
@@ -3103,7 +3107,7 @@ bool shadow_flush_tlb(bool (*flush_vcpu)(void *ctxt, struct vcpu *v),
     {
         unsigned int cpu;
 
-        if ( !flush_vcpu(ctxt, v) )
+        if ( !flush_vcpu(v, vcpu_bitmap) )
             continue;
 
         paging_update_cr3(v, false);
@@ -3118,7 +3122,7 @@ bool shadow_flush_tlb(bool (*flush_vcpu)(void *ctxt, struct vcpu *v),
 
     /* Done. */
     for_each_vcpu ( d, v )
-        if ( v != current && flush_vcpu(ctxt, v) )
+        if ( v != current && flush_vcpu(v, vcpu_bitmap) )
             vcpu_unpause(v);
 
     return true;
diff --git a/xen/arch/x86/mm/shadow/private.h b/xen/arch/x86/mm/shadow/private.h
index 35efb1b984fb..e4db8d32546a 100644
--- a/xen/arch/x86/mm/shadow/private.h
+++ b/xen/arch/x86/mm/shadow/private.h
@@ -922,8 +922,7 @@ static inline int sh_check_page_has_no_refs(struct page_info *page)
 }
 
 /* Flush the TLB of the selected vCPUs. */
-bool shadow_flush_tlb(bool (*flush_vcpu)(void *ctxt, struct vcpu *v),
-                      void *ctxt);
+bool shadow_flush_tlb(const unsigned long *vcpu_bitmap);
 
 #endif /* _XEN_SHADOW_PRIVATE_H */
 
diff --git a/xen/include/asm-x86/paging.h b/xen/include/asm-x86/paging.h
index 996c2cd0383f..308f1115dde9 100644
--- a/xen/include/asm-x86/paging.h
+++ b/xen/include/asm-x86/paging.h
@@ -141,9 +141,7 @@ struct paging_mode {
     void          (*update_cr3            )(struct vcpu *v, int do_locking,
                                             bool noflush);
     void          (*update_paging_modes   )(struct vcpu *v);
-    bool          (*flush_tlb             )(bool (*flush_vcpu)(void *ctxt,
-                                                               struct vcpu *v),
-                                            void *ctxt);
+    bool          (*flush_tlb             )(const unsigned long *vcpu_bitmap);
 
     unsigned int guest_levels;
 
@@ -417,11 +415,10 @@ static always_inline unsigned int paging_max_paddr_bits(const struct domain *d)
     return bits;
 }
 
-static inline bool paging_flush_tlb(bool (*flush_vcpu)(void *ctxt,
-                                                       struct vcpu *v),
-                                    void *ctxt)
+/* Flush selected vCPUs TLBs.  NULL for all. */
+static inline bool paging_flush_tlb(const unsigned long *vcpu_bitmap)
 {
-    return paging_get_hostmode(current)->flush_tlb(flush_vcpu, ctxt);
+    return paging_get_hostmode(current)->flush_tlb(vcpu_bitmap);
 }
 
 #endif /* XEN_PAGING_H */
-- 
2.11.0


Re: [PATCH] x86/hvm: Remove callback from paging->flush_tlb() hook

Posted by Jan Beulich 2 weeks, 3 days ago
On 17.11.2021 19:26, Andrew Cooper wrote:
> TLB flushing is a hotpath, and function pointer calls are
> expensive (especially under repoline) for what amounts to an identity
> transform on the data.  Just pass the vcpu_bitmap bitmap directly.
> 
> As we use NULL for all rather than none, introduce a flush_vcpu() helper to
> avoid the risk of logical errors from opencoding the expression.  This also
> means the viridian callers can avoid writing an all-ones bitmap for the
> flushing logic to consume.

I think you want to clarify that you convert only one of the two ways of
specifying "all". The other (HV_GENERIC_SET_ALL as consumed by
hv_vpset_to_vpmask()) could also be converted, but this would be a bit
more involved. I have no idea which of the two Windows would typically
use, nor why there are two mechanisms in the first place.

> No functional change.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>

Jan


Re: [PATCH] x86/hvm: Remove callback from paging->flush_tlb() hook

Posted by Andrew Cooper 2 weeks, 3 days ago
On 18/11/2021 10:45, Jan Beulich wrote:
> On 17.11.2021 19:26, Andrew Cooper wrote:
>> TLB flushing is a hotpath, and function pointer calls are
>> expensive (especially under repoline) for what amounts to an identity
>> transform on the data.  Just pass the vcpu_bitmap bitmap directly.
>>
>> As we use NULL for all rather than none, introduce a flush_vcpu() helper to
>> avoid the risk of logical errors from opencoding the expression.  This also
>> means the viridian callers can avoid writing an all-ones bitmap for the
>> flushing logic to consume.
> I think you want to clarify that you convert only one of the two ways of
> specifying "all". The other (HV_GENERIC_SET_ALL as consumed by
> hv_vpset_to_vpmask()) could also be converted, but this would be a bit
> more involved. I have no idea which of the two Windows would typically
> use, nor why there are two mechanisms in the first place.

Oh - I'd not spotted that path.  It is well hidden away from
HV_FLUSH_ALL_PROCESSORS.

Giving how windows APIs typically evolve,
HVCALL_FLUSH_VIRTUAL_ADDRESS_{SPACE,LIST} where first.  It has a limit
of 64 vCPUs, and the VpSet sparse form is clearly catering to massive
numbers of vCPUs.

I'd expect to see both paths used, so we ought to see about optimising
that too, in due course.

>> No functional change.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Reviewed-by: Jan Beulich <jbeulich@suse.com>

Thanks.

~Andrew

Re: [PATCH] x86/hvm: Remove callback from paging->flush_tlb() hook

Posted by Durrant, Paul 2 weeks, 3 days ago
On 18/11/2021 11:19, Andrew Cooper wrote:
> On 18/11/2021 10:45, Jan Beulich wrote:
>> On 17.11.2021 19:26, Andrew Cooper wrote:
>>> TLB flushing is a hotpath, and function pointer calls are
>>> expensive (especially under repoline) for what amounts to an identity
>>> transform on the data.  Just pass the vcpu_bitmap bitmap directly.
>>>
>>> As we use NULL for all rather than none, introduce a flush_vcpu() helper to
>>> avoid the risk of logical errors from opencoding the expression.  This also
>>> means the viridian callers can avoid writing an all-ones bitmap for the
>>> flushing logic to consume.
>> I think you want to clarify that you convert only one of the two ways of
>> specifying "all". The other (HV_GENERIC_SET_ALL as consumed by
>> hv_vpset_to_vpmask()) could also be converted, but this would be a bit
>> more involved. I have no idea which of the two Windows would typically
>> use, nor why there are two mechanisms in the first place.
> 
> Oh - I'd not spotted that path.  It is well hidden away from
> HV_FLUSH_ALL_PROCESSORS.
> 
> Giving how windows APIs typically evolve,
> HVCALL_FLUSH_VIRTUAL_ADDRESS_{SPACE,LIST} where first.  It has a limit
> of 64 vCPUs, and the VpSet sparse form is clearly catering to massive
> numbers of vCPUs.
> 
> I'd expect to see both paths used, so we ought to see about optimising
> that too, in due course.
> 

In my experience, yes, it only uses the sparse version if you have more 
than 64 vCPUs.

   Paul

>>> No functional change.
>>>
>>> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
>> Reviewed-by: Jan Beulich <jbeulich@suse.com>
> 
> Thanks.
> 
> ~Andrew
> 


[PATCH v2] x86/hvm: Remove callback from paging->flush_tlb() hook

Posted by Andrew Cooper 2 weeks, 3 days ago
TLB flushing is a hotpath, and function pointer calls are
expensive (especially under repoline) for what amounts to an identity
transform on the data.  Just pass the vcpu_bitmap bitmap directly.

As we use NULL for all rather than none, introduce a flush_vcpu() helper to
avoid the risk of logical errors from opencoding the expression.  This also
means the viridian callers can avoid writing an all-ones bitmap for the
flushing logic to consume.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Wei Liu <wl@xen.org>
CC: Paul Durrant <paul@xen.org>

v2:
 * Also short-circuit the hvcall_flush_ex() HV_GENERIC_SET_ALL path.

The result even compiles smaller:

  $ ../scripts/bloat-o-meter xen-syms-before xen-syms-after
  add/remove: 0/2 grow/shrink: 0/3 up/down: 0/-125 (-125)
  Function                                     old     new   delta
  flush_tlb                                    207     205      -2
  always_flush                                   6       -      -6
  need_flush                                     9       -      -9
  do_hvm_op                                   2434    2418     -16
  shadow_flush_tlb                             628     536     -92

but this is very much not the point of the patch.

It would be rather more efficient in this case and probably others for
for_each_vcpu() to iterate over d->vcpu[] than follow the v->next_vcpu pointer
chain (better locality of access), and also because then the vCPU id is the
loop induction variable, not a value read from memory.
---
 xen/arch/x86/hvm/hvm.c               |  7 +------
 xen/arch/x86/hvm/viridian/viridian.c | 34 +++++++++++-----------------------
 xen/arch/x86/mm/hap/hap.c            | 11 ++++++++---
 xen/arch/x86/mm/shadow/common.c      | 18 +++++++++++-------
 xen/arch/x86/mm/shadow/private.h     |  3 +--
 xen/include/asm-x86/paging.h         | 11 ++++-------
 6 files changed, 36 insertions(+), 48 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index eee365711d63..31e9474db093 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4047,17 +4047,12 @@ static void hvm_s3_resume(struct domain *d)
     }
 }
 
-static bool always_flush(void *ctxt, struct vcpu *v)
-{
-    return true;
-}
-
 static int hvmop_flush_tlb_all(void)
 {
     if ( !is_hvm_domain(current->domain) )
         return -EINVAL;
 
-    return paging_flush_tlb(always_flush, NULL) ? 0 : -ERESTART;
+    return paging_flush_tlb(NULL) ? 0 : -ERESTART;
 }
 
 static int hvmop_set_evtchn_upcall_vector(
diff --git a/xen/arch/x86/hvm/viridian/viridian.c b/xen/arch/x86/hvm/viridian/viridian.c
index b906f7b86a74..51d50e194e6d 100644
--- a/xen/arch/x86/hvm/viridian/viridian.c
+++ b/xen/arch/x86/hvm/viridian/viridian.c
@@ -574,13 +574,6 @@ static void vpmask_fill(struct hypercall_vpmask *vpmask)
     bitmap_fill(vpmask->mask, HVM_MAX_VCPUS);
 }
 
-static bool vpmask_test(const struct hypercall_vpmask *vpmask,
-                        unsigned int vp)
-{
-    ASSERT(vp < HVM_MAX_VCPUS);
-    return test_bit(vp, vpmask->mask);
-}
-
 static unsigned int vpmask_first(const struct hypercall_vpmask *vpmask)
 {
     return find_first_bit(vpmask->mask, HVM_MAX_VCPUS);
@@ -669,17 +662,6 @@ static uint16_t hv_vpset_to_vpmask(const struct hv_vpset *set,
 #undef NR_VPS_PER_BANK
 }
 
-/*
- * Windows should not issue the hypercalls requiring this callback in the
- * case where vcpu_id would exceed the size of the mask.
- */
-static bool need_flush(void *ctxt, struct vcpu *v)
-{
-    struct hypercall_vpmask *vpmask = ctxt;
-
-    return vpmask_test(vpmask, v->vcpu_id);
-}
-
 union hypercall_input {
     uint64_t raw;
     struct {
@@ -714,6 +696,7 @@ static int hvcall_flush(const union hypercall_input *input,
         uint64_t flags;
         uint64_t vcpu_mask;
     } input_params;
+    unsigned long *vcpu_bitmap;
 
     /* These hypercalls should never use the fast-call convention. */
     if ( input->fast )
@@ -730,18 +713,19 @@ static int hvcall_flush(const union hypercall_input *input,
      * so err on the safe side.
      */
     if ( input_params.flags & HV_FLUSH_ALL_PROCESSORS )
-        vpmask_fill(vpmask);
+        vcpu_bitmap = NULL;
     else
     {
         vpmask_empty(vpmask);
         vpmask_set(vpmask, 0, input_params.vcpu_mask);
+        vcpu_bitmap = vpmask->mask;
     }
 
     /*
      * A false return means that another vcpu is currently trying
      * a similar operation, so back off.
      */
-    if ( !paging_flush_tlb(need_flush, vpmask) )
+    if ( !paging_flush_tlb(vcpu_bitmap) )
         return -ERESTART;
 
     output->rep_complete = input->rep_count;
@@ -760,6 +744,7 @@ static int hvcall_flush_ex(const union hypercall_input *input,
         uint64_t flags;
         struct hv_vpset set;
     } input_params;
+    unsigned long *vcpu_bitmap;
 
     /* These hypercalls should never use the fast-call convention. */
     if ( input->fast )
@@ -770,8 +755,9 @@ static int hvcall_flush_ex(const union hypercall_input *input,
                                   sizeof(input_params)) != HVMTRANS_okay )
         return -EINVAL;
 
-    if ( input_params.flags & HV_FLUSH_ALL_PROCESSORS )
-        vpmask_fill(vpmask);
+    if ( input_params.flags & HV_FLUSH_ALL_PROCESSORS ||
+         input_params.set.format == HV_GENERIC_SET_ALL )
+        vcpu_bitmap = NULL;
     else
     {
         union hypercall_vpset *vpset = &this_cpu(hypercall_vpset);
@@ -807,13 +793,15 @@ static int hvcall_flush_ex(const union hypercall_input *input,
         rc = hv_vpset_to_vpmask(set, vpmask);
         if ( rc )
             return rc;
+
+        vcpu_bitmap = vpmask->mask;
     }
 
     /*
      * A false return means that another vcpu is currently trying
      * a similar operation, so back off.
      */
-    if ( !paging_flush_tlb(need_flush, vpmask) )
+    if ( !paging_flush_tlb(vcpu_bitmap) )
         return -ERESTART;
 
     output->rep_complete = input->rep_count;
diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
index 5b269ef8b3bb..de4b13565ab4 100644
--- a/xen/arch/x86/mm/hap/hap.c
+++ b/xen/arch/x86/mm/hap/hap.c
@@ -696,8 +696,13 @@ static void hap_update_cr3(struct vcpu *v, int do_locking, bool noflush)
     hvm_update_guest_cr3(v, noflush);
 }
 
-static bool flush_tlb(bool (*flush_vcpu)(void *ctxt, struct vcpu *v),
-                      void *ctxt)
+static bool flush_vcpu(const struct vcpu *v, const unsigned long *vcpu_bitmap)
+{
+    return !vcpu_bitmap || test_bit(v->vcpu_id, vcpu_bitmap);
+}
+
+/* Flush TLB of selected vCPUs.  NULL for all. */
+static bool flush_tlb(const unsigned long *vcpu_bitmap)
 {
     static DEFINE_PER_CPU(cpumask_t, flush_cpumask);
     cpumask_t *mask = &this_cpu(flush_cpumask);
@@ -712,7 +717,7 @@ static bool flush_tlb(bool (*flush_vcpu)(void *ctxt, struct vcpu *v),
     {
         unsigned int cpu;
 
-        if ( !flush_vcpu(ctxt, v) )
+        if ( !flush_vcpu(v, vcpu_bitmap) )
             continue;
 
         hvm_asid_flush_vcpu(v);
diff --git a/xen/arch/x86/mm/shadow/common.c b/xen/arch/x86/mm/shadow/common.c
index 8c1b041f7135..de09ef5cae58 100644
--- a/xen/arch/x86/mm/shadow/common.c
+++ b/xen/arch/x86/mm/shadow/common.c
@@ -3069,9 +3069,13 @@ static void sh_clean_dirty_bitmap(struct domain *d)
 }
 
 
-/* Fluhs TLB of selected vCPUs. */
-bool shadow_flush_tlb(bool (*flush_vcpu)(void *ctxt, struct vcpu *v),
-                      void *ctxt)
+static bool flush_vcpu(const struct vcpu *v, const unsigned long *vcpu_bitmap)
+{
+    return !vcpu_bitmap || test_bit(v->vcpu_id, vcpu_bitmap);
+}
+
+/* Flush TLB of selected vCPUs.  NULL for all. */
+bool shadow_flush_tlb(const unsigned long *vcpu_bitmap)
 {
     static DEFINE_PER_CPU(cpumask_t, flush_cpumask);
     cpumask_t *mask = &this_cpu(flush_cpumask);
@@ -3084,12 +3088,12 @@ bool shadow_flush_tlb(bool (*flush_vcpu)(void *ctxt, struct vcpu *v),
 
     /* Pause all other vcpus. */
     for_each_vcpu ( d, v )
-        if ( v != current && flush_vcpu(ctxt, v) )
+        if ( v != current && flush_vcpu(v, vcpu_bitmap) )
             vcpu_pause_nosync(v);
 
     /* Now that all VCPUs are signalled to deschedule, we wait... */
     for_each_vcpu ( d, v )
-        if ( v != current && flush_vcpu(ctxt, v) )
+        if ( v != current && flush_vcpu(v, vcpu_bitmap) )
             while ( !vcpu_runnable(v) && v->is_running )
                 cpu_relax();
 
@@ -3103,7 +3107,7 @@ bool shadow_flush_tlb(bool (*flush_vcpu)(void *ctxt, struct vcpu *v),
     {
         unsigned int cpu;
 
-        if ( !flush_vcpu(ctxt, v) )
+        if ( !flush_vcpu(v, vcpu_bitmap) )
             continue;
 
         paging_update_cr3(v, false);
@@ -3118,7 +3122,7 @@ bool shadow_flush_tlb(bool (*flush_vcpu)(void *ctxt, struct vcpu *v),
 
     /* Done. */
     for_each_vcpu ( d, v )
-        if ( v != current && flush_vcpu(ctxt, v) )
+        if ( v != current && flush_vcpu(v, vcpu_bitmap) )
             vcpu_unpause(v);
 
     return true;
diff --git a/xen/arch/x86/mm/shadow/private.h b/xen/arch/x86/mm/shadow/private.h
index 35efb1b984fb..e4db8d32546a 100644
--- a/xen/arch/x86/mm/shadow/private.h
+++ b/xen/arch/x86/mm/shadow/private.h
@@ -922,8 +922,7 @@ static inline int sh_check_page_has_no_refs(struct page_info *page)
 }
 
 /* Flush the TLB of the selected vCPUs. */
-bool shadow_flush_tlb(bool (*flush_vcpu)(void *ctxt, struct vcpu *v),
-                      void *ctxt);
+bool shadow_flush_tlb(const unsigned long *vcpu_bitmap);
 
 #endif /* _XEN_SHADOW_PRIVATE_H */
 
diff --git a/xen/include/asm-x86/paging.h b/xen/include/asm-x86/paging.h
index 996c2cd0383f..308f1115dde9 100644
--- a/xen/include/asm-x86/paging.h
+++ b/xen/include/asm-x86/paging.h
@@ -141,9 +141,7 @@ struct paging_mode {
     void          (*update_cr3            )(struct vcpu *v, int do_locking,
                                             bool noflush);
     void          (*update_paging_modes   )(struct vcpu *v);
-    bool          (*flush_tlb             )(bool (*flush_vcpu)(void *ctxt,
-                                                               struct vcpu *v),
-                                            void *ctxt);
+    bool          (*flush_tlb             )(const unsigned long *vcpu_bitmap);
 
     unsigned int guest_levels;
 
@@ -417,11 +415,10 @@ static always_inline unsigned int paging_max_paddr_bits(const struct domain *d)
     return bits;
 }
 
-static inline bool paging_flush_tlb(bool (*flush_vcpu)(void *ctxt,
-                                                       struct vcpu *v),
-                                    void *ctxt)
+/* Flush selected vCPUs TLBs.  NULL for all. */
+static inline bool paging_flush_tlb(const unsigned long *vcpu_bitmap)
 {
-    return paging_get_hostmode(current)->flush_tlb(flush_vcpu, ctxt);
+    return paging_get_hostmode(current)->flush_tlb(vcpu_bitmap);
 }
 
 #endif /* XEN_PAGING_H */
-- 
2.11.0


Re: [PATCH v2] x86/hvm: Remove callback from paging->flush_tlb() hook

Posted by Durrant, Paul 2 weeks, 3 days ago
On 18/11/2021 18:48, Andrew Cooper wrote:
> TLB flushing is a hotpath, and function pointer calls are
> expensive (especially under repoline) for what amounts to an identity
> transform on the data.  Just pass the vcpu_bitmap bitmap directly.
> 
> As we use NULL for all rather than none, introduce a flush_vcpu() helper to
> avoid the risk of logical errors from opencoding the expression.  This also
> means the viridian callers can avoid writing an all-ones bitmap for the
> flushing logic to consume.
> 
> No functional change.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Reviewed-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Paul Durrant <paul@xen.org>