[PATCH] x86/hvm: Drop .is_singlestep_supported() callback

[PATCH] x86/hvm: Drop .is_singlestep_supported() callback

[Andrew Cooper]

There is absolutely no need for a function pointer call here.

Drop the hook, introduce a singlestep_supported boolean, and configure it in
start_vmx() like all other optional functionality.

No functional change, but rather more efficient logic.

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: Tamas K Lengyel <tamas@tklengyel.com>
CC: Jun Nakajima <jun.nakajima@intel.com>
CC: Kevin Tian <kevin.tian@intel.com>

Based on Jan's "altcall all hvm ops" patch, but not logically related.  This
had escaped my previous attempts to drop inappropriate function pointer use.

The hvm_funcs data fields are a mess.  All the booleans and 'hvm_capabilities'
want merging into a single bitfield, so we're not wasting 8 bytes of space to
hold 6 bits of information.
---
 xen/arch/x86/hvm/vmx/vmx.c         | 8 ++------
 xen/arch/x86/include/asm/hvm/hvm.h | 7 +++----
 2 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index a7a0d662342a..1c46669762b0 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2120,11 +2120,6 @@ static void vmx_enable_msr_interception(struct domain *d, uint32_t msr)
         vmx_set_msr_intercept(v, msr, VMX_MSR_W);
 }
 
-static bool_t vmx_is_singlestep_supported(void)
-{
-    return !!cpu_has_monitor_trap_flag;
-}
-
 static void vmx_vcpu_update_eptp(struct vcpu *v)
 {
     struct domain *d = v->domain;
@@ -2454,7 +2449,6 @@ static struct hvm_function_table __initdata vmx_function_table = {
     .nhvm_domain_relinquish_resources = nvmx_domain_relinquish_resources,
     .nhvm_hap_walk_L1_p2m = nvmx_hap_walk_L1_p2m,
     .enable_msr_interception = vmx_enable_msr_interception,
-    .is_singlestep_supported = vmx_is_singlestep_supported,
     .altp2m_vcpu_update_p2m = vmx_vcpu_update_eptp,
     .altp2m_vcpu_update_vmfunc_ve = vmx_vcpu_update_vmfunc_ve,
     .altp2m_vcpu_emulate_ve = vmx_vcpu_emulate_ve,
@@ -2661,6 +2655,8 @@ const struct hvm_function_table * __init start_vmx(void)
         return NULL;
     }
 
+    vmx_function_table.singlestep_supported = cpu_has_monitor_trap_flag;
+
     if ( cpu_has_vmx_dt_exiting )
         vmx_function_table.set_descriptor_access_exiting =
             vmx_set_descriptor_access_exiting;
diff --git a/xen/arch/x86/include/asm/hvm/hvm.h b/xen/arch/x86/include/asm/hvm/hvm.h
index b26302d9e769..9338cf25a657 100644
--- a/xen/arch/x86/include/asm/hvm/hvm.h
+++ b/xen/arch/x86/include/asm/hvm/hvm.h
@@ -97,6 +97,7 @@ struct hvm_function_table {
 
     /* Necessary hardware support for alternate p2m's? */
     bool altp2m_supported;
+    bool singlestep_supported;
 
     /* Hardware virtual interrupt delivery enable? */
     bool virtual_intr_delivery_enabled;
@@ -208,7 +209,6 @@ struct hvm_function_table {
                                 uint8_t *p2m_acc, struct npfec npfec);
 
     void (*enable_msr_interception)(struct domain *d, uint32_t msr);
-    bool_t (*is_singlestep_supported)(void);
 
     /* Alternate p2m */
     void (*altp2m_vcpu_update_p2m)(struct vcpu *v);
@@ -644,10 +644,9 @@ static inline void hvm_enable_msr_interception(struct domain *d, uint32_t msr)
     alternative_vcall(hvm_funcs.enable_msr_interception, d, msr);
 }
 
-static inline bool_t hvm_is_singlestep_supported(void)
+static inline bool hvm_is_singlestep_supported(void)
 {
-    return (hvm_funcs.is_singlestep_supported &&
-            alternative_call(hvm_funcs.is_singlestep_supported));
+    return hvm_funcs.singlestep_supported;
 }
 
 static inline bool hvm_hap_supported(void)
-- 
2.11.0

Re: [PATCH] x86/hvm: Drop .is_singlestep_supported() callback

[Jan Beulich]

On 13.01.2022 19:48, Andrew Cooper wrote:
> There is absolutely no need for a function pointer call here.
> 
> Drop the hook, introduce a singlestep_supported boolean, and configure it in
> start_vmx() like all other optional functionality.
> 
> No functional change, but rather more efficient logic.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

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

Re: [PATCH] x86/hvm: Drop .is_singlestep_supported() callback

[Tamas K Lengyel]

On Thu, Jan 13, 2022 at 1:48 PM Andrew Cooper <andrew.cooper3@citrix.com> wrote:
>
> There is absolutely no need for a function pointer call here.
>
> Drop the hook, introduce a singlestep_supported boolean, and configure it in
> start_vmx() like all other optional functionality.
>
> No functional change, but rather more efficient logic.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Reviewed-by: Tamas K Lengyel <tamas@tklengyel.com>