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Date:   Wed, 4 Jan 2023 11:56:32 -0600
From:   Michael Roth <michael.roth@amd.com>
To:     Jarkko Sakkinen <jarkko@kernel.org>
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Subject: Re: [PATCH RFC v7 02/64] KVM: x86: Add
 KVM_CAP_UNMAPPED_PRIVATE_MEMORY
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On Wed, Jan 04, 2023 at 12:03:44PM +0000, Jarkko Sakkinen wrote:
> On Wed, Dec 14, 2022 at 01:39:54PM -0600, Michael Roth wrote:
> > This mainly indicates to KVM that it should expect all private guest
> > memory to be backed by private memslots. Ideally this would work
> > similarly for others archs, give or take a few additional flags, but
> > for now it's a simple boolean indicator for x86.
> > 
> > Signed-off-by: Michael Roth <michael.roth@amd.com>
> > ---
> >  arch/x86/include/asm/kvm_host.h |  3 +++
> >  arch/x86/kvm/x86.c              | 10 ++++++++++
> >  include/uapi/linux/kvm.h        |  1 +
> >  3 files changed, 14 insertions(+)
> > 
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 27ef31133352..2b6244525107 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -1438,6 +1438,9 @@ struct kvm_arch {
> >  	 */
> >  #define SPLIT_DESC_CACHE_MIN_NR_OBJECTS (SPTE_ENT_PER_PAGE + 1)
> >  	struct kvm_mmu_memory_cache split_desc_cache;
> > +
> > +	/* Use/enforce unmapped private memory. */
> > +	bool upm_mode;
> >  };
> >  
> >  struct kvm_vm_stat {
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index c67e22f3e2ee..99ecf99bc4d2 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -4421,6 +4421,11 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> >  	case KVM_CAP_EXIT_HYPERCALL:
> >  		r = KVM_EXIT_HYPERCALL_VALID_MASK;
> >  		break;
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +	case KVM_CAP_UNMAPPED_PRIVATE_MEM:
> > +		r = 1;
> > +		break;
> > +#endif
> >  	case KVM_CAP_SET_GUEST_DEBUG2:
> >  		return KVM_GUESTDBG_VALID_MASK;
> >  #ifdef CONFIG_KVM_XEN
> > @@ -6382,6 +6387,10 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> >  		}
> >  		mutex_unlock(&kvm->lock);
> >  		break;
> > +	case KVM_CAP_UNMAPPED_PRIVATE_MEM:
> > +		kvm->arch.upm_mode = true;
> > +		r = 0;
> > +		break;
> >  	default:
> >  		r = -EINVAL;
> >  		break;
> > @@ -12128,6 +12137,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> >  	kvm->arch.default_tsc_khz = max_tsc_khz ? : tsc_khz;
> >  	kvm->arch.guest_can_read_msr_platform_info = true;
> >  	kvm->arch.enable_pmu = enable_pmu;
> > +	kvm->arch.upm_mode = false;
> >  
> >  #if IS_ENABLED(CONFIG_HYPERV)
> >  	spin_lock_init(&kvm->arch.hv_root_tdp_lock);
> > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > index c7e9d375a902..cc9424ccf9b2 100644
> > --- a/include/uapi/linux/kvm.h
> > +++ b/include/uapi/linux/kvm.h
> > @@ -1219,6 +1219,7 @@ struct kvm_ppc_resize_hpt {
> >  #define KVM_CAP_DIRTY_LOG_RING_ACQ_REL 223
> >  #define KVM_CAP_S390_PROTECTED_ASYNC_DISABLE 224
> >  #define KVM_CAP_MEMORY_ATTRIBUTES 225
> > +#define KVM_CAP_UNMAPPED_PRIVATE_MEM 240
> >  
> >  #ifdef KVM_CAP_IRQ_ROUTING
> >  
> > -- 
> > 2.25.1
> > 
> 
> Why we want to carry non-UPM support still?

For SNP, non-UPM support is no longer included in this patchset.

However, this patchset also adds support for UPM-based SEV (for lazy-pinning
support). So we still need a way to let userspace switch between those 2
modes.

-Mike

> 
> BR, Jarkko
>