Re: [PATCH v6 08/14] KVM: X86: Introduce KVM_HC_PAGE_ENC_STATUS hypercall

[Ashish Kalra]

On Fri, Apr 03, 2020 at 01:57:48AM +0000, Ashish Kalra wrote:
> On Thu, Apr 02, 2020 at 06:31:54PM -0700, Krish Sadhukhan wrote:
> > 
> > On 3/29/20 11:22 PM, Ashish Kalra wrote:
> > > From: Brijesh Singh <Brijesh.Singh@xxxxxxx>
> > > 
> > > This hypercall is used by the SEV guest to notify a change in the page
> > > encryption status to the hypervisor. The hypercall should be invoked
> > > only when the encryption attribute is changed from encrypted -> decrypted
> > > and vice versa. By default all guest pages are considered encrypted.
> > > 
> > > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> > > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > > Cc: "Radim KrÄmÃÅ" <rkrcmar@xxxxxxxxxx>
> > > Cc: Joerg Roedel <joro@xxxxxxxxxx>
> > > Cc: Borislav Petkov <bp@xxxxxxx>
> > > Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
> > > Cc: x86@xxxxxxxxxx
> > > Cc: kvm@xxxxxxxxxxxxxxx
> > > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > > Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> > > Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> > > ---
> > >   Documentation/virt/kvm/hypercalls.rst | 15 +++++
> > >   arch/x86/include/asm/kvm_host.h       |  2 +
> > >   arch/x86/kvm/svm.c                    | 95 +++++++++++++++++++++++++++
> > >   arch/x86/kvm/vmx/vmx.c                |  1 +
> > >   arch/x86/kvm/x86.c                    |  6 ++
> > >   include/uapi/linux/kvm_para.h         |  1 +
> > >   6 files changed, 120 insertions(+)
> > > 
> > > diff --git a/Documentation/virt/kvm/hypercalls.rst b/Documentation/virt/kvm/hypercalls.rst
> > > index dbaf207e560d..ff5287e68e81 100644
> > > --- a/Documentation/virt/kvm/hypercalls.rst
> > > +++ b/Documentation/virt/kvm/hypercalls.rst
> > > @@ -169,3 +169,18 @@ a0: destination APIC ID
> > >   :Usage example: When sending a call-function IPI-many to vCPUs, yield if
> > >   	        any of the IPI target vCPUs was preempted.
> > > +
> > > +
> > > +8. KVM_HC_PAGE_ENC_STATUS
> > > +-------------------------
> > > +:Architecture: x86
> > > +:Status: active
> > > +:Purpose: Notify the encryption status changes in guest page table (SEV guest)
> > > +
> > > +a0: the guest physical address of the start page
> > > +a1: the number of pages
> > > +a2: encryption attribute
> > > +
> > > +   Where:
> > > +	* 1: Encryption attribute is set
> > > +	* 0: Encryption attribute is cleared
> > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > > index 98959e8cd448..90718fa3db47 100644
> > > --- a/arch/x86/include/asm/kvm_host.h
> > > +++ b/arch/x86/include/asm/kvm_host.h
> > > @@ -1267,6 +1267,8 @@ struct kvm_x86_ops {
> > >   	bool (*apic_init_signal_blocked)(struct kvm_vcpu *vcpu);
> > >   	int (*enable_direct_tlbflush)(struct kvm_vcpu *vcpu);
> > > +	int (*page_enc_status_hc)(struct kvm *kvm, unsigned long gpa,
> > > +				  unsigned long sz, unsigned long mode);
> > >   };
> > >   struct kvm_arch_async_pf {
> > > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> > > index 7c2721e18b06..1d8beaf1bceb 100644
> > > --- a/arch/x86/kvm/svm.c
> > > +++ b/arch/x86/kvm/svm.c
> > > @@ -136,6 +136,8 @@ struct kvm_sev_info {
> > >   	int fd;			/* SEV device fd */
> > >   	unsigned long pages_locked; /* Number of pages locked */
> > >   	struct list_head regions_list;  /* List of registered regions */
> > > +	unsigned long *page_enc_bmap;
> > > +	unsigned long page_enc_bmap_size;
> > >   };
> > >   struct kvm_svm {
> > > @@ -1991,6 +1993,9 @@ static void sev_vm_destroy(struct kvm *kvm)
> > >   	sev_unbind_asid(kvm, sev->handle);
> > >   	sev_asid_free(sev->asid);
> > > +
> > > +	kvfree(sev->page_enc_bmap);
> > > +	sev->page_enc_bmap = NULL;
> > >   }
> > >   static void avic_vm_destroy(struct kvm *kvm)
> > > @@ -7593,6 +7598,94 @@ static int sev_receive_finish(struct kvm *kvm, struct kvm_sev_cmd *argp)
> > >   	return ret;
> > >   }
> > > +static int sev_resize_page_enc_bitmap(struct kvm *kvm, unsigned long new_size)
> > > +{
> > > +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> > > +	unsigned long *map;
> > > +	unsigned long sz;
> > > +
> > > +	if (sev->page_enc_bmap_size >= new_size)
> > > +		return 0;
> > > +
> > > +	sz = ALIGN(new_size, BITS_PER_LONG) / 8;
> > > +
> > > +	map = vmalloc(sz);
> > 
> > 
> > Just wondering why we can't directly modify sev->page_enc_bmap.
> > 
> 
> Because the page_enc_bitmap needs to be re-sized here, it needs to be
> expanded here. 
> 

I don't believe there is anything is like a realloc() kind of equivalent
for the kmalloc() interfaces.

Thanks,
Ashish

> > > +	if (!map) {
> > > +		pr_err_once("Failed to allocate encrypted bitmap size %lx\n",
> > > +				sz);
> > > +		return -ENOMEM;
> > > +	}
> > > +
> > > +	/* mark the page encrypted (by default) */
> > > +	memset(map, 0xff, sz);
> > > +
> > > +	bitmap_copy(map, sev->page_enc_bmap, sev->page_enc_bmap_size);
> > > +	kvfree(sev->page_enc_bmap);
> > > +
> > > +	sev->page_enc_bmap = map;
> > > +	sev->page_enc_bmap_size = new_size;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static int svm_page_enc_status_hc(struct kvm *kvm, unsigned long gpa,
> > > +				  unsigned long npages, unsigned long enc)
> > > +{
> > > +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> > > +	kvm_pfn_t pfn_start, pfn_end;
> > > +	gfn_t gfn_start, gfn_end;
> > > +	int ret;
> > > +
> > > +	if (!sev_guest(kvm))
> > > +		return -EINVAL;
> > > +
> > > +	if (!npages)
> > > +		return 0;
> > > +
> > > +	gfn_start = gpa_to_gfn(gpa);
> > > +	gfn_end = gfn_start + npages;
> > > +
> > > +	/* out of bound access error check */
> > > +	if (gfn_end <= gfn_start)
> > > +		return -EINVAL;
> > > +
> > > +	/* lets make sure that gpa exist in our memslot */
> > > +	pfn_start = gfn_to_pfn(kvm, gfn_start);
> > > +	pfn_end = gfn_to_pfn(kvm, gfn_end);
> > > +
> > > +	if (is_error_noslot_pfn(pfn_start) && !is_noslot_pfn(pfn_start)) {
> > > +		/*
> > > +		 * Allow guest MMIO range(s) to be added
> > > +		 * to the page encryption bitmap.
> > > +		 */
> > > +		return -EINVAL;
> > > +	}
> > > +
> > > +	if (is_error_noslot_pfn(pfn_end) && !is_noslot_pfn(pfn_end)) {
> > > +		/*
> > > +		 * Allow guest MMIO range(s) to be added
> > > +		 * to the page encryption bitmap.
> > > +		 */
> > > +		return -EINVAL;
> > > +	}
> > 
> > 
> > It seems is_error_noslot_pfn() covers both cases - i) gfn slot is absent,
> > ii) failure to translate to pfn. So do we still need is_noslot_pfn() ?
> >
> 
> We do need to check for !is_noslot_pfn(..) additionally as the MMIO ranges will not
> be having a slot allocated.
> 
> Thanks,
> Ashish
> 
> > > +
> > > +	mutex_lock(&kvm->lock);
> > > +	ret = sev_resize_page_enc_bitmap(kvm, gfn_end);
> > > +	if (ret)
> > > +		goto unlock;
> > > +
> > > +	if (enc)
> > > +		__bitmap_set(sev->page_enc_bmap, gfn_start,
> > > +				gfn_end - gfn_start);
> > > +	else
> > > +		__bitmap_clear(sev->page_enc_bmap, gfn_start,
> > > +				gfn_end - gfn_start);
> > > +
> > > +unlock:
> > > +	mutex_unlock(&kvm->lock);
> > > +	return ret;
> > > +}
> > > +
> > >   static int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
> > >   {
> > >   	struct kvm_sev_cmd sev_cmd;
> > > @@ -7995,6 +8088,8 @@ static struct kvm_x86_ops svm_x86_ops __ro_after_init = {
> > >   	.need_emulation_on_page_fault = svm_need_emulation_on_page_fault,
> > >   	.apic_init_signal_blocked = svm_apic_init_signal_blocked,
> > > +
> > > +	.page_enc_status_hc = svm_page_enc_status_hc,
> > 
> > 
> > Why not place it where other encryption ops are located ?
> > 
> > ÂÂÂ ÂÂÂ ...
> > 
> > ÂÂÂ ÂÂÂ .mem_enc_unreg_region
> > 
> > +Â ÂÂÂ .page_enc_status_hc = svm_page_enc_status_hc
> > 
> > >   };
> > >   static int __init svm_init(void)
> > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > > index 079d9fbf278e..f68e76ee7f9c 100644
> > > --- a/arch/x86/kvm/vmx/vmx.c
> > > +++ b/arch/x86/kvm/vmx/vmx.c
> > > @@ -8001,6 +8001,7 @@ static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
> > >   	.nested_get_evmcs_version = NULL,
> > >   	.need_emulation_on_page_fault = vmx_need_emulation_on_page_fault,
> > >   	.apic_init_signal_blocked = vmx_apic_init_signal_blocked,
> > > +	.page_enc_status_hc = NULL,
> > >   };
> > >   static void vmx_cleanup_l1d_flush(void)
> > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > > index cf95c36cb4f4..68428eef2dde 100644
> > > --- a/arch/x86/kvm/x86.c
> > > +++ b/arch/x86/kvm/x86.c
> > > @@ -7564,6 +7564,12 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
> > >   		kvm_sched_yield(vcpu->kvm, a0);
> > >   		ret = 0;
> > >   		break;
> > > +	case KVM_HC_PAGE_ENC_STATUS:
> > > +		ret = -KVM_ENOSYS;
> > > +		if (kvm_x86_ops->page_enc_status_hc)
> > > +			ret = kvm_x86_ops->page_enc_status_hc(vcpu->kvm,
> > > +					a0, a1, a2);
> > > +		break;
> > >   	default:
> > >   		ret = -KVM_ENOSYS;
> > >   		break;
> > > diff --git a/include/uapi/linux/kvm_para.h b/include/uapi/linux/kvm_para.h
> > > index 8b86609849b9..847b83b75dc8 100644
> > > --- a/include/uapi/linux/kvm_para.h
> > > +++ b/include/uapi/linux/kvm_para.h
> > > @@ -29,6 +29,7 @@
> > >   #define KVM_HC_CLOCK_PAIRING		9
> > >   #define KVM_HC_SEND_IPI		10
> > >   #define KVM_HC_SCHED_YIELD		11
> > > +#define KVM_HC_PAGE_ENC_STATUS		12
> > >   /*
> > >    * hypercalls use architecture specific