Re: [PATCH 4/4] KVM: VMX: Resurrect vmcs_conf sanitization for KVM-on-Hyper-V

[Sean Christopherson]

On Tue, Oct 18, 2022, Vitaly Kuznetsov wrote:
> @@ -362,6 +364,7 @@ uint16_t nested_get_evmcs_version(struct kvm_vcpu *vcpu)
>  
>  enum evmcs_revision {
>  	EVMCSv1_LEGACY,
> +	EVMCSv1_STRICT,

"strict" isn't really the right word, this is more like "raw" or "unfiltered",
because unless I'm misunderstanding the intent, this will always track KVM's
bleeding edge, i.e. everything that KVM can possibly enable.

And in that case, we can avoid bikeshedding the name becase bouncing through
evmcs_supported_ctrls is unnecessary, just use the #defines directly.  And then
you can just fold the one (or two) #defines from patch 3 into this path.

> @@ -511,6 +525,52 @@ int nested_evmcs_check_controls(struct vmcs12 *vmcs12)
>  	return 0;
>  }
>  
> +#if IS_ENABLED(CONFIG_HYPERV)
> +/*
> + * KVM on Hyper-V always uses the newest known eVMCSv1 revision, the assumption
> + * is: in case a feature has corresponding fields in eVMCS described and it was
> + * exposed in VMX feature MSRs, KVM is free to use it. Warn if KVM meets a
> + * feature which has no corresponding eVMCS field, this likely means that KVM
> + * needs to be updated.
> + */
> +#define evmcs_check_vmcs_conf32(field, ctrl)					\
> +	{									\
> +		u32 supported, unsupported32;					\
> +										\
> +		supported = evmcs_get_supported_ctls(ctrl, EVMCSv1_STRICT);	\
> +		unsupported32 = vmcs_conf->field & ~supported;			\
> +		if (unsupported32) {						\
> +			pr_warn_once(#field " unsupported with eVMCS: 0x%x\n",	\
> +				     unsupported32);				\
> +			vmcs_conf->field &= supported;				\
> +		}								\
> +	}
> +
> +#define evmcs_check_vmcs_conf64(field, ctrl)					\
> +	{									\
> +		u32 supported;							\
> +		u64 unsupported64;						\

Channeling my inner Morpheus: Stop trying to use macros and use macros!  :-D

---
 arch/x86/kvm/vmx/evmcs.c | 34 ++++++++++++++++++++++++++++++++++
 arch/x86/kvm/vmx/evmcs.h |  2 ++
 arch/x86/kvm/vmx/vmx.c   |  5 +++++
 3 files changed, 41 insertions(+)

diff --git a/arch/x86/kvm/vmx/evmcs.c b/arch/x86/kvm/vmx/evmcs.c
index 337783675731..f7f8eafeecf7 100644
--- a/arch/x86/kvm/vmx/evmcs.c
+++ b/arch/x86/kvm/vmx/evmcs.c
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
+#define pr_fmt(fmt) "kvm/hyper-v: " fmt
+
 #include <linux/errno.h>
 #include <linux/smp.h>
 
@@ -507,6 +509,38 @@ int nested_evmcs_check_controls(struct vmcs12 *vmcs12)
 	return 0;
 }
 
+#if IS_ENABLED(CONFIG_HYPERV)
+/*
+ * KVM on Hyper-V always uses the newest known eVMCSv1 revision, the assumption
+ * is: in case a feature has corresponding fields in eVMCS described and it was
+ * exposed in VMX feature MSRs, KVM is free to use it. Warn if KVM meets a
+ * feature which has no corresponding eVMCS field, this likely means that KVM
+ * needs to be updated.
+ */
+#define evmcs_check_vmcs_conf(field, ctrl)				\
+do {									\
+	typeof(vmcs_conf->field) unsupported;				\
+									\
+	unsupported = vmcs_conf->field & EVMCS1_UNSUPPORTED_ ## ctrl;	\
+	if (unsupported) {						\
+		pr_warn_once(#field " unsupported with eVMCS: 0x%llx\n",\
+			     (u64)unsupported);				\
+		vmcs_conf->field &= ~unsupported;			\
+	}								\
+}									\
+while (0)
+
+__init void evmcs_sanitize_exec_ctrls(struct vmcs_config *vmcs_conf)
+{
+	evmcs_check_vmcs_conf(cpu_based_exec_ctrl, EXEC_CTRL);
+	evmcs_check_vmcs_conf(pin_based_exec_ctrl, PINCTRL);
+	evmcs_check_vmcs_conf(cpu_based_2nd_exec_ctrl, 2NDEXEC);
+	evmcs_check_vmcs_conf(cpu_based_3rd_exec_ctrl, 3RDEXEC);
+	evmcs_check_vmcs_conf(vmentry_ctrl, VMENTRY_CTRL);
+	evmcs_check_vmcs_conf(vmexit_ctrl, VMEXIT_CTRL);
+}
+#endif
+
 int nested_enable_evmcs(struct kvm_vcpu *vcpu,
 			uint16_t *vmcs_version)
 {
diff --git a/arch/x86/kvm/vmx/evmcs.h b/arch/x86/kvm/vmx/evmcs.h
index 6f746ef3c038..bc795c6e9059 100644
--- a/arch/x86/kvm/vmx/evmcs.h
+++ b/arch/x86/kvm/vmx/evmcs.h
@@ -58,6 +58,7 @@ DECLARE_STATIC_KEY_FALSE(enable_evmcs);
 	 SECONDARY_EXEC_SHADOW_VMCS |					\
 	 SECONDARY_EXEC_TSC_SCALING |					\
 	 SECONDARY_EXEC_PAUSE_LOOP_EXITING)
+#define EVMCS1_UNSUPPORTED_3RDEXEC (~0ULL)
 #define EVMCS1_UNSUPPORTED_VMEXIT_CTRL					\
 	(VM_EXIT_SAVE_VMX_PREEMPTION_TIMER)
 #define EVMCS1_UNSUPPORTED_VMENTRY_CTRL (0)
@@ -209,6 +210,7 @@ static inline void evmcs_load(u64 phys_addr)
 	vp_ap->enlighten_vmentry = 1;
 }
 
+__init void evmcs_sanitize_exec_ctrls(struct vmcs_config *vmcs_conf);
 #else /* !IS_ENABLED(CONFIG_HYPERV) */
 static __always_inline void evmcs_write64(unsigned long field, u64 value) {}
 static inline void evmcs_write32(unsigned long field, u32 value) {}
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 9dba04b6b019..7fd21b1fae1d 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2720,6 +2720,11 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
 	vmcs_conf->vmentry_ctrl        = _vmentry_control;
 	vmcs_conf->misc	= misc_msr;
 
+#if IS_ENABLED(CONFIG_HYPERV)
+	if (enlightened_vmcs)
+		evmcs_sanitize_exec_ctrls(vmcs_conf);
+#endif
+
 	return 0;
 }
 

base-commit: 5b6b6bcc0ef138b55fdd17dc8f9d43dfd26f8bd7
--