Re: [PATCH 4/6] x86,hyperv: Clean up hv_do_hypercall()

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Apr 21, 2025 at 06:27:57PM +0000, Michael Kelley wrote:

> > @@ -483,14 +484,16 @@ static void __init ms_hyperv_init_platfo
> >  			ms_hyperv.shared_gpa_boundary =
> >  				BIT_ULL(ms_hyperv.shared_gpa_boundary_bits);
> > 
> > -		hyperv_paravisor_present = !!ms_hyperv.paravisor_present;
> > -
> >  		pr_info("Hyper-V: Isolation Config: Group A 0x%x, Group B 0x%x\n",
> >  			ms_hyperv.isolation_config_a, ms_hyperv.isolation_config_b);
> > 
> > 
> >  		if (hv_get_isolation_type() == HV_ISOLATION_TYPE_SNP) {
> >  			static_branch_enable(&isolation_type_snp);
> > +#if defined(CONFIG_AMD_MEM_ENCRYPT) && defined(CONFIG_HYPERV)
> > +			if (!ms_hyperv.paravisor_present)
> > +				static_call_update(hv_hypercall, hv_snp_hypercall);
> > +#endif
> 
> This #ifdef (and one below for TDX) are really ugly. They could be avoided by adding
> stubs for hv_snp_hypercall() and hv_tdx_hypercall(), and making the hv_hypercall static
> call exist even when !CONFIG_HYPERV (and for 32-bit builds). Or is there a reason to
> not do that?
> 
> >  		} else if (hv_get_isolation_type() == HV_ISOLATION_TYPE_TDX) {
> >  			static_branch_enable(&isolation_type_tdx);
> > 
> > @@ -498,6 +501,9 @@ static void __init ms_hyperv_init_platfo
> >  			ms_hyperv.hints &= ~HV_X64_APIC_ACCESS_RECOMMENDED;
> > 
> >  			if (!ms_hyperv.paravisor_present) {
> > +#if defined(CONFIG_INTEL_TDX_GUEST) && defined(CONFIG_HYPERV)
> > +				static_call_update(hv_hypercall, hv_tdx_hypercall);
> > +#endif
> >  				/*
> >  				 * Mark the Hyper-V TSC page feature as disabled
> >  				 * in a TDX VM without paravisor so that the
> > 
> > 

I've ended up with the below.. I thought it a waste to make all that
stuff available to 32bit and !HYPERV.


--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c
@@ -392,6 +392,7 @@ u64 hv_snp_hypercall(u64 control, u64 pa
 #else
 static inline void hv_ghcb_msr_write(u64 msr, u64 value) {}
 static inline void hv_ghcb_msr_read(u64 msr, u64 *value) {}
+u64 hv_snp_hypercall(u64 control, u64 param1, u64 param2) {}
 #endif /* CONFIG_AMD_MEM_ENCRYPT */
 
 #ifdef CONFIG_INTEL_TDX_GUEST
@@ -441,6 +442,7 @@ u64 hv_tdx_hypercall(u64 control, u64 pa
 #else
 static inline void hv_tdx_msr_write(u64 msr, u64 value) {}
 static inline void hv_tdx_msr_read(u64 msr, u64 *value) {}
+u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2) {}
 #endif /* CONFIG_INTEL_TDX_GUEST */
 
 #if defined(CONFIG_AMD_MEM_ENCRYPT) || defined(CONFIG_INTEL_TDX_GUEST)
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -39,6 +39,10 @@ static inline unsigned char hv_get_nmi_r
 	return 0;
 }
 
+extern u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2);
+extern u64 hv_snp_hypercall(u64 control, u64 param1, u64 param2);
+extern u64 hv_std_hypercall(u64 control, u64 param1, u64 param2);
+
 #if IS_ENABLED(CONFIG_HYPERV)
 extern void *hv_hypercall_pg;
 
@@ -48,10 +52,6 @@ bool hv_isolation_type_snp(void);
 bool hv_isolation_type_tdx(void);
 
 #ifdef CONFIG_X86_64
-extern u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2);
-extern u64 hv_snp_hypercall(u64 control, u64 param1, u64 param2);
-extern u64 hv_std_hypercall(u64 control, u64 param1, u64 param2);
-
 DECLARE_STATIC_CALL(hv_hypercall, hv_std_hypercall);
 #endif
 
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -287,9 +287,14 @@ static void __init x86_setup_ops_for_tsc
 #ifdef CONFIG_X86_64
 DEFINE_STATIC_CALL(hv_hypercall, hv_std_hypercall);
 EXPORT_STATIC_CALL_TRAMP_GPL(hv_hypercall);
+#define hypercall_update(hc) static_call_update(hv_hypercall, hc)
 #endif
 #endif /* CONFIG_HYPERV */
 
+#ifndef hypercall_update
+#define hypercall_update(hc) (void)hc
+#endif
+
 static uint32_t  __init ms_hyperv_platform(void)
 {
 	u32 eax;
@@ -490,10 +495,8 @@ static void __init ms_hyperv_init_platfo
 
 		if (hv_get_isolation_type() == HV_ISOLATION_TYPE_SNP) {
 			static_branch_enable(&isolation_type_snp);
-#if defined(CONFIG_AMD_MEM_ENCRYPT) && defined(CONFIG_HYPERV)
 			if (!ms_hyperv.paravisor_present)
-				static_call_update(hv_hypercall, hv_snp_hypercall);
-#endif
+				hypercall_update(hv_snp_hypercall);
 		} else if (hv_get_isolation_type() == HV_ISOLATION_TYPE_TDX) {
 			static_branch_enable(&isolation_type_tdx);
 
@@ -501,9 +504,7 @@ static void __init ms_hyperv_init_platfo
 			ms_hyperv.hints &= ~HV_X64_APIC_ACCESS_RECOMMENDED;
 
 			if (!ms_hyperv.paravisor_present) {
-#if defined(CONFIG_INTEL_TDX_GUEST) && defined(CONFIG_HYPERV)
-				static_call_update(hv_hypercall, hv_tdx_hypercall);
-#endif
+				hypercall_update(hv_tdx_hypercall);
 				/*
 				 * Mark the Hyper-V TSC page feature as disabled
 				 * in a TDX VM without paravisor so that the