Re: [PATCH AUTOSEL for 4.14 12/67] KVM: x86: add support for emulating UMIP

[Paolo Bonzini]

----- Original Message -----
> From: "Sasha Levin" <Alexander.Levin@xxxxxxxxxxxxx>
> To: linux-kernel@xxxxxxxxxxxxxxx, stable@xxxxxxxxxxxxxxx
> Cc: "Paolo Bonzini" <pbonzini@xxxxxxxxxx>, "Sasha Levin" <Alexander.Levin@xxxxxxxxxxxxx>
> Sent: Thursday, March 8, 2018 5:57:36 AM
> Subject: [PATCH AUTOSEL for 4.14 12/67] KVM: x86: add support for emulating UMIP
> 
> From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> 
> [ Upstream commit 66336cab3531d3325ebde36a04725dddd0c42cb5 ]
> 
> The User-Mode Instruction Prevention feature present in recent Intel
> processor prevents a group of instructions (sgdt, sidt, sldt, smsw, and
> str) from being executed with CPL > 0. Otherwise, a general protection
> fault is issued.
> 
> UMIP instructions in general are also able to trigger vmexits, so we can
> actually emulate UMIP on older processors.  This commit sets up the
> infrastructure so that kvm-intel.ko and kvm-amd.ko can set the UMIP
> feature bit for CPUID even if the feature is not actually available
> in hardware.
> 
> Reviewed-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>

This is not enough (there were a couple bugs, plus you have not
added the changes needed to the handle SLDT, STR, etc. in the
emulator).  But since this is a feature, why is it being backported
to 4.14, especially without any testing??

Thanks,

Paolo

> ---
>  arch/x86/include/asm/kvm_host.h | 1 +
>  arch/x86/kvm/cpuid.c            | 2 ++
>  arch/x86/kvm/svm.c              | 6 ++++++
>  arch/x86/kvm/vmx.c              | 6 ++++++
>  4 files changed, 15 insertions(+)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h
> b/arch/x86/include/asm/kvm_host.h
> index 4f8b80199672..52ecf9b2f61e 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1004,6 +1004,7 @@ struct kvm_x86_ops {
>  	void (*handle_external_intr)(struct kvm_vcpu *vcpu);
>  	bool (*mpx_supported)(void);
>  	bool (*xsaves_supported)(void);
> +	bool (*umip_emulated)(void);
>  
>  	int (*check_nested_events)(struct kvm_vcpu *vcpu, bool external_intr);
>  
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 13f5d4217e4f..f3fc225f5ebb 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -325,6 +325,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2
> *entry, u32 function,
>  	unsigned f_invpcid = kvm_x86_ops->invpcid_supported() ? F(INVPCID) : 0;
>  	unsigned f_mpx = kvm_mpx_supported() ? F(MPX) : 0;
>  	unsigned f_xsaves = kvm_x86_ops->xsaves_supported() ? F(XSAVES) : 0;
> +	unsigned f_umip = kvm_x86_ops->umip_emulated() ? F(UMIP) : 0;
>  
>  	/* cpuid 1.edx */
>  	const u32 kvm_cpuid_1_edx_x86_features =
> @@ -476,6 +477,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2
> *entry, u32 function,
>  			entry->ebx |= F(TSC_ADJUST);
>  			entry->ecx &= kvm_cpuid_7_0_ecx_x86_features;
>  			cpuid_mask(&entry->ecx, CPUID_7_ECX);
> +			entry->ecx |= f_umip;
>  			/* PKU is not yet implemented for shadow paging. */
>  			if (!tdp_enabled || !boot_cpu_has(X86_FEATURE_OSPKE))
>  				entry->ecx &= ~F(PKU);
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index e0bc3ad0f6cd..8ea19bf09202 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -5322,6 +5322,11 @@ static bool svm_xsaves_supported(void)
>  	return false;
>  }
>  
> +static bool svm_umip_emulated(void)
> +{
> +	return false;
> +}
> +
>  static bool svm_has_wbinvd_exit(void)
>  {
>  	return true;
> @@ -5633,6 +5638,7 @@ static struct kvm_x86_ops svm_x86_ops __ro_after_init =
> {
>  	.invpcid_supported = svm_invpcid_supported,
>  	.mpx_supported = svm_mpx_supported,
>  	.xsaves_supported = svm_xsaves_supported,
> +	.umip_emulated = svm_umip_emulated,
>  
>  	.set_supported_cpuid = svm_set_supported_cpuid,
>  
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 5ffde16253cb..924d88d5ca35 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -9212,6 +9212,11 @@ static bool vmx_xsaves_supported(void)
>  		SECONDARY_EXEC_XSAVES;
>  }
>  
> +static bool vmx_umip_emulated(void)
> +{
> +	return false;
> +}
> +
>  static void vmx_recover_nmi_blocking(struct vcpu_vmx *vmx)
>  {
>  	u32 exit_intr_info;
> @@ -12252,6 +12257,7 @@ static struct kvm_x86_ops vmx_x86_ops __ro_after_init
> = {
>  	.handle_external_intr = vmx_handle_external_intr,
>  	.mpx_supported = vmx_mpx_supported,
>  	.xsaves_supported = vmx_xsaves_supported,
> +	.umip_emulated = vmx_umip_emulated,
>  
>  	.check_nested_events = vmx_check_nested_events,
>  
> --
> 2.14.1
>