KVM needs to check if guests can see RRSBA_CTRL. If a guest is using
retpoline and cannot see RRSBA_CTRL and the host enumerates RRSBA,
KVM is responsible for setting RRSBA_DIS_S for the guest.

This allows VM migration from parts doesn't enumerates RRSBA to those
that enumerate RRSBA.

Signed-off-by: Zhang Chen <chen.zhang@intel.com>
---
 arch/x86/kvm/cpuid.c         | 4 ++++
 arch/x86/kvm/reverse_cpuid.h | 7 +++++++
 2 files changed, 11 insertions(+)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 62bc7a01cecc..8d45bc0b4b7c 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -668,6 +668,10 @@ void kvm_set_cpu_caps(void)
 		SF(SGX1) | SF(SGX2)
 	);
 
+	kvm_cpu_cap_init_scattered(CPUID_7_2_EDX,
+		SF(RRSBA_CTRL)
+	);
+
 	kvm_cpu_cap_mask(CPUID_8000_0001_ECX,
 		F(LAHF_LM) | F(CMP_LEGACY) | 0 /*SVM*/ | 0 /* ExtApicSpace */ |
 		F(CR8_LEGACY) | F(ABM) | F(SSE4A) | F(MISALIGNSSE) |
diff --git a/arch/x86/kvm/reverse_cpuid.h b/arch/x86/kvm/reverse_cpuid.h
index a19d473d0184..4c38ed61c505 100644
--- a/arch/x86/kvm/reverse_cpuid.h
+++ b/arch/x86/kvm/reverse_cpuid.h
@@ -13,6 +13,7 @@
  */
 enum kvm_only_cpuid_leafs {
 	CPUID_12_EAX	 = NCAPINTS,
+	CPUID_7_2_EDX,
 	NR_KVM_CPU_CAPS,
 
 	NKVMCAPINTS = NR_KVM_CPU_CAPS - NCAPINTS,
@@ -24,6 +25,9 @@ enum kvm_only_cpuid_leafs {
 #define KVM_X86_FEATURE_SGX1		KVM_X86_FEATURE(CPUID_12_EAX, 0)
 #define KVM_X86_FEATURE_SGX2		KVM_X86_FEATURE(CPUID_12_EAX, 1)
 
+/* Intel-defined sub-features, CPUID level 0x00000007:2 (EDX)*/
+#define KVM_X86_FEATURE_RRSBA_CTRL	KVM_X86_FEATURE(CPUID_7_2_EDX, 2)
+
 struct cpuid_reg {
 	u32 function;
 	u32 index;
@@ -46,6 +50,7 @@ static const struct cpuid_reg reverse_cpuid[] = {
 	[CPUID_8000_0007_EBX] = {0x80000007, 0, CPUID_EBX},
 	[CPUID_7_EDX]         = {         7, 0, CPUID_EDX},
 	[CPUID_7_1_EAX]       = {         7, 1, CPUID_EAX},
+	[CPUID_7_2_EDX]       = {         7, 2, CPUID_EDX},
 	[CPUID_12_EAX]        = {0x00000012, 0, CPUID_EAX},
 	[CPUID_8000_001F_EAX] = {0x8000001f, 0, CPUID_EAX},
 };
@@ -78,6 +83,8 @@ static __always_inline u32 __feature_translate(int x86_feature)
 		return KVM_X86_FEATURE_SGX1;
 	else if (x86_feature == X86_FEATURE_SGX2)
 		return KVM_X86_FEATURE_SGX2;
+	else if (x86_feature == X86_FEATURE_RRSBA_CTRL)
+		return KVM_X86_FEATURE_RRSBA_CTRL;
 
 	return x86_feature;
 }
-- 
2.25.1

On Sun, Dec 11, 2022 at 12:00:39AM +0800, Zhang Chen wrote:
> KVM needs to check if guests can see RRSBA_CTRL. If a guest is using
> retpoline and cannot see RRSBA_CTRL and the host enumerates RRSBA,
> KVM is responsible for setting RRSBA_DIS_S for the guest.
> 
> This allows VM migration from parts doesn't enumerates RRSBA to those

perhaps s/parts doesn't enumerates/parts that do not enumerate/ reads
better?

> that enumerate RRSBA.

and here maybe s/that enumerate RRSBA/do/ ?

Thanks and BR,
Ricardo

> -----Original Message-----
> From: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> Sent: Thursday, December 15, 2022 5:34 AM
> To: Zhang, Chen <chen.zhang@intel.com>
> Cc: x86@kernel.org; linux-kernel@vger.kernel.org; kvm@vger.kernel.org; Gao,
> Chao <chao.gao@intel.com>; Pawan Gupta
> <pawan.kumar.gupta@linux.intel.com>; Paolo Bonzini
> <pbonzini@redhat.com>; Christopherson,, Sean <seanjc@google.com>; H.
> Peter Anvin <hpa@zytor.com>; Dave Hansen <dave.hansen@linux.intel.com>;
> Borislav Petkov <bp@alien8.de>; Ingo Molnar <mingo@redhat.com>; Thomas
> Gleixner <tglx@linutronix.de>
> Subject: Re: [RFC PATCH 2/9] KVM: x86: Add a kvm-only leaf for RRSBA_CTRL
> 
> On Sun, Dec 11, 2022 at 12:00:39AM +0800, Zhang Chen wrote:
> > KVM needs to check if guests can see RRSBA_CTRL. If a guest is using
> > retpoline and cannot see RRSBA_CTRL and the host enumerates RRSBA, KVM
> > is responsible for setting RRSBA_DIS_S for the guest.
> >
> > This allows VM migration from parts doesn't enumerates RRSBA to those
> 
> perhaps s/parts doesn't enumerates/parts that do not enumerate/ reads
> better?

OK.

> 
> > that enumerate RRSBA.
> 
> and here maybe s/that enumerate RRSBA/do/ ?

Looks good to me. Thanks for your comments.
I will fix patch2/3 in the next version.

Thanks
Chen

> 
> Thanks and BR,
> Ricardo