Re: [PATCH v7 012/102] KVM: x86: Introduce vm_type to differentiate default VMs from confidential VMs

[Kai Huang <kai.huang@intel.com>]

On Tue, 2022-06-28 at 14:52 +1200, Kai Huang wrote:
> On Mon, 2022-06-27 at 14:53 -0700, isaku.yamahata@intel.com wrote:
> > From: Sean Christopherson <sean.j.christopherson@intel.com>
> > 
> > Unlike default VMs, confidential VMs (Intel TDX and AMD SEV-ES) don't allow
> > some operations (e.g., memory read/write, register state access, etc).
> > 
> > Introduce vm_type to track the type of the VM to x86 KVM.  Other arch KVMs
> > already use vm_type, KVM_INIT_VM accepts vm_type, and x86 KVM callback
> > vm_init accepts vm_type.  So follow them.  Further, a different policy can
> > be made based on vm_type.  Define KVM_X86_DEFAULT_VM for default VM as
> > default and define KVM_X86_TDX_VM for Intel TDX VM.  The wrapper function
> > will be defined as "bool is_td(kvm) { return vm_type == VM_TYPE_TDX; }"
> > 
> > Add a capability KVM_CAP_VM_TYPES to effectively allow device model,
> > e.g. qemu, to query what VM types are supported by KVM.  This (introduce a
> > new capability and add vm_type) is chosen to align with other arch KVMs
> > that have VM types already.  Other arch KVMs uses different name to query
> > supported vm types and there is no common name for it, so new name was
> > chosen.
> > 
> > Co-developed-by: Xiaoyao Li <xiaoyao.li@intel.com>
> > Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> > Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> > ---
> >  Documentation/virt/kvm/api.rst        | 21 +++++++++++++++++++++
> >  arch/x86/include/asm/kvm-x86-ops.h    |  1 +
> >  arch/x86/include/asm/kvm_host.h       |  2 ++
> >  arch/x86/include/uapi/asm/kvm.h       |  3 +++
> >  arch/x86/kvm/svm/svm.c                |  6 ++++++
> >  arch/x86/kvm/vmx/main.c               |  1 +
> >  arch/x86/kvm/vmx/tdx.h                |  6 +-----
> >  arch/x86/kvm/vmx/vmx.c                |  5 +++++
> >  arch/x86/kvm/vmx/x86_ops.h            |  1 +
> >  arch/x86/kvm/x86.c                    |  9 ++++++++-
> >  include/uapi/linux/kvm.h              |  1 +
> >  tools/arch/x86/include/uapi/asm/kvm.h |  3 +++
> >  tools/include/uapi/linux/kvm.h        |  1 +
> >  13 files changed, 54 insertions(+), 6 deletions(-)
> > 
> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > index 9cbbfdb663b6..b9ab598883b2 100644
> > --- a/Documentation/virt/kvm/api.rst
> > +++ b/Documentation/virt/kvm/api.rst
> > @@ -147,10 +147,31 @@ described as 'basic' will be available.
> >  The new VM has no virtual cpus and no memory.
> >  You probably want to use 0 as machine type.
> >  
> > +X86:
> > +^^^^
> > +
> > +Supported vm type can be queried from KVM_CAP_VM_TYPES, which returns the
> > +bitmap of supported vm types. The 1-setting of bit @n means vm type with
> > +value @n is supported.
> 
> 
> Perhaps I am missing something, but I don't understand how the below changes
> (except the x86 part above) in Documentation are related to this patch.
> 
> > +
> > +S390:
> > +^^^^^
> > +
> >  In order to create user controlled virtual machines on S390, check
> >  KVM_CAP_S390_UCONTROL and use the flag KVM_VM_S390_UCONTROL as
> >  privileged user (CAP_SYS_ADMIN).
> >  
> > +MIPS:
> > +^^^^^
> > +
> > +To use hardware assisted virtualization on MIPS (VZ ASE) rather than
> > +the default trap & emulate implementation (which changes the virtual
> > +memory layout to fit in user mode), check KVM_CAP_MIPS_VZ and use the
> > +flag KVM_VM_MIPS_VZ.
> > +
> > +ARM64:
> > +^^^^^^
> > +
> >  On arm64, the physical address size for a VM (IPA Size limit) is limited
> >  to 40bits by default. The limit can be configured if the host supports the
> >  extension KVM_CAP_ARM_VM_IPA_SIZE. When supported, use
> > diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
> > index 75bc44aa8d51..a97cdb203a16 100644
> > --- a/arch/x86/include/asm/kvm-x86-ops.h
> > +++ b/arch/x86/include/asm/kvm-x86-ops.h
> > @@ -19,6 +19,7 @@ KVM_X86_OP(hardware_disable)
> >  KVM_X86_OP(hardware_unsetup)
> >  KVM_X86_OP(has_emulated_msr)
> >  KVM_X86_OP(vcpu_after_set_cpuid)
> > +KVM_X86_OP(is_vm_type_supported)
> >  KVM_X86_OP(vm_init)
> >  KVM_X86_OP_OPTIONAL(vm_destroy)
> >  KVM_X86_OP_OPTIONAL_RET0(vcpu_precreate)
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index aa11525500d3..089e0a4de926 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -1141,6 +1141,7 @@ enum kvm_apicv_inhibit {
> >  };
> >  
> >  struct kvm_arch {
> > +	unsigned long vm_type;
> >  	unsigned long n_used_mmu_pages;
> >  	unsigned long n_requested_mmu_pages;
> >  	unsigned long n_max_mmu_pages;
> > @@ -1434,6 +1435,7 @@ struct kvm_x86_ops {
> >  	bool (*has_emulated_msr)(struct kvm *kvm, u32 index);
> >  	void (*vcpu_after_set_cpuid)(struct kvm_vcpu *vcpu);
> >  
> > +	bool (*is_vm_type_supported)(unsigned long vm_type);
> >  	unsigned int vm_size;
> >  	int (*vm_init)(struct kvm *kvm);
> >  	void (*vm_destroy)(struct kvm *kvm);
> > diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
> > index 50a4e787d5e6..9792ec1cc317 100644
> > --- a/arch/x86/include/uapi/asm/kvm.h
> > +++ b/arch/x86/include/uapi/asm/kvm.h
> > @@ -531,4 +531,7 @@ struct kvm_pmu_event_filter {
> >  #define KVM_VCPU_TSC_CTRL 0 /* control group for the timestamp counter (TSC) */
> >  #define   KVM_VCPU_TSC_OFFSET 0 /* attribute for the TSC offset */
> >  
> > +#define KVM_X86_DEFAULT_VM	0
> > +#define KVM_X86_TDX_VM		1
> > +
> >  #endif /* _ASM_X86_KVM_H */
> > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> > index 247c0ad458a0..815a07c594f1 100644
> > --- a/arch/x86/kvm/svm/svm.c
> > +++ b/arch/x86/kvm/svm/svm.c
> > @@ -4685,6 +4685,11 @@ static void svm_vm_destroy(struct kvm *kvm)
> >  	sev_vm_destroy(kvm);
> >  }
> >  
> > +static bool svm_is_vm_type_supported(unsigned long type)
> > +{
> > +	return type == KVM_X86_DEFAULT_VM;
> > +}
> > +
> >  static int svm_vm_init(struct kvm *kvm)
> >  {
> >  	if (!pause_filter_count || !pause_filter_thresh)
> > @@ -4712,6 +4717,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
> >  	.vcpu_free = svm_vcpu_free,
> >  	.vcpu_reset = svm_vcpu_reset,
> >  
> > +	.is_vm_type_supported = svm_is_vm_type_supported,
> >  	.vm_size = sizeof(struct kvm_svm),
> >  	.vm_init = svm_vm_init,
> >  	.vm_destroy = svm_vm_destroy,
> > diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
> > index ac788af17d92..7be4941e4c4d 100644
> > --- a/arch/x86/kvm/vmx/main.c
> > +++ b/arch/x86/kvm/vmx/main.c
> > @@ -43,6 +43,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
> >  	.hardware_disable = vmx_hardware_disable,
> >  	.has_emulated_msr = vmx_has_emulated_msr,
> >  
> > +	.is_vm_type_supported = vmx_is_vm_type_supported,
> >  	.vm_size = sizeof(struct kvm_vmx),
> >  	.vm_init = vmx_vm_init,
> >  	.vm_destroy = vmx_vm_destroy,
> > diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
> > index 54d7a26ed9ee..2f43db5bbefb 100644
> > --- a/arch/x86/kvm/vmx/tdx.h
> > +++ b/arch/x86/kvm/vmx/tdx.h
> > @@ -17,11 +17,7 @@ struct vcpu_tdx {
> >  
> >  static inline bool is_td(struct kvm *kvm)
> >  {
> > -	/*
> > -	 * TDX VM type isn't defined yet.
> > -	 * return kvm->arch.vm_type == KVM_X86_TDX_VM;
> > -	 */
> > -	return false;
> > +	return kvm->arch.vm_type == KVM_X86_TDX_VM;
> >  }
> 
> If you put this patch before patch:
> 
> 	[PATCH v7 009/102] KVM: TDX: Add placeholders for TDX VM/vcpu structure
> 
> Then you don't need to introduce this chunk in above patch and then remove it
> here, which is unnecessary and ugly.
> 
> And you can even only introduce KVM_X86_DEFAULT_VM but not KVM_X86_TDX_VM in
> this patch, so you can make this patch as a infrastructural patch to report VM
> type.  The KVM_X86_TDX_VM can come with the patch where is_td() is introduced
> (in your above patch 9).  
> 
> To me, it's more clean way to write patch.  For instance, this infrastructural
> patch can be theoretically used by other series if they have similar thing to
> support, but doesn't need to carry is_td() and KVM_X86_TDX_VM burden that you
> made.

Sorry I missed this patch already has Paolo's Reviewed-by.  Please feel free to
ignore my comments.


-- 
Thanks,
-Kai