Re: [Qemu-devel] [RFC PATCH v1 08/10] KVM: X86: Introduce KVM_HC_PAGE_ENC_STATUS hypercall

["Lendacky, Thomas" <Thomas.Lendacky@amd.com>]

On 4/24/19 11:10 AM, Singh, Brijesh wrote:
> The hypercall can be used by the SEV guest to notify the page encryption

This hyercall is used by the SEV guest to notify a change in the page...

> 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 the guest pages should be considered encrypted.

By default all guest page are considered

> 
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: "Radim Krčmář" <rkrcmar@redhat.com>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: x86@kernel.org
> Cc: kvm@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
>  Documentation/virtual/kvm/hypercalls.txt | 14 +++++
>  arch/x86/include/asm/kvm_host.h          |  2 +
>  arch/x86/kvm/svm.c                       | 69 ++++++++++++++++++++++++
>  arch/x86/kvm/vmx/vmx.c                   |  1 +
>  arch/x86/kvm/x86.c                       |  5 ++
>  include/uapi/linux/kvm_para.h            |  1 +
>  6 files changed, 92 insertions(+)
> 
> diff --git a/Documentation/virtual/kvm/hypercalls.txt b/Documentation/virtual/kvm/hypercalls.txt
> index da24c138c8d1..ecd44e488679 100644
> --- a/Documentation/virtual/kvm/hypercalls.txt
> +++ b/Documentation/virtual/kvm/hypercalls.txt
> @@ -141,3 +141,17 @@ a0 corresponds to the APIC ID in the third argument (a2), bit 1
>  corresponds to the APIC ID a2+1, and so on.
>  
>  Returns the number of CPUs to which the IPIs were delivered successfully.
> +
> +7. 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: set or clear the encryption attribute

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 a9d03af34030..adb0ca035b97 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1196,6 +1196,8 @@ struct kvm_x86_ops {
>  	uint16_t (*nested_get_evmcs_version)(struct kvm_vcpu *vcpu);
>  
>  	bool (*need_emulation_on_page_fault)(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 74b57ab742ad..f024f208b052 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -138,6 +138,8 @@ 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 {
> @@ -1911,6 +1913,8 @@ static void sev_vm_destroy(struct kvm *kvm)
>  
>  	sev_unbind_asid(kvm, sev->handle);
>  	sev_asid_free(kvm);
> +
> +	kvfree(sev->page_enc_bmap);
>  }
>  
>  static void avic_vm_destroy(struct kvm *kvm)
> @@ -7370,6 +7374,69 @@ 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;
> +
> +	if (sz > PAGE_SIZE)
> +		map = vmalloc(sz);
> +	else
> +		map = kmalloc(sz, GFP_KERNEL);

Any reason this can't always be vmalloc()?

> +
> +	if (!map) {
> +		pr_err_once("Failed to allocate decrypted bitmap size %lx\n", sz);
> +		return 1;

Should this be -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;
> +	gfn_t gfn_start, gfn_end;
> +	int r;

int ret; ?  "r" at first confused me.

> +
> +	if (!npages)
> +		return 0;
> +
> +	gfn_start = gpa_to_gfn(gpa);
> +	gfn_end = gfn_start + npages;
> +
> +	mutex_lock(&kvm->lock);
> +
> +	r = 1;
> +	if (sev_resize_page_enc_bitmap(kvm, gfn_end))

ret = sev_resize_...
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);
> +
> +	r = 0;

If you do the above, this is not needed.

Thanks,
Tom

> +unlock:
> +	mutex_unlock(&kvm->lock);
> +	return r;
> +}
> +
>  static int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
>  {
>  	struct kvm_sev_cmd sev_cmd;
> @@ -7711,6 +7778,8 @@ static struct kvm_x86_ops svm_x86_ops __ro_after_init = {
>  	.nested_get_evmcs_version = nested_get_evmcs_version,
>  
>  	.need_emulation_on_page_fault = svm_need_emulation_on_page_fault,
> +
> +	.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 b4e7d645275a..9c814e560e0f 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7731,6 +7731,7 @@ static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
>  	.get_vmcs12_pages = NULL,
>  	.nested_enable_evmcs = NULL,
>  	.need_emulation_on_page_fault = vmx_need_emulation_on_page_fault,
> +	.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 a0d1fc80ac5a..dea644be5992 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7141,6 +7141,11 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
>  	case KVM_HC_SEND_IPI:
>  		ret = kvm_pv_send_ipi(vcpu->kvm, a0, a1, a2, a3, op_64_bit);
>  		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 6c0ce49931e5..3dc9e579f4f9 100644
> --- a/include/uapi/linux/kvm_para.h
> +++ b/include/uapi/linux/kvm_para.h
> @@ -28,6 +28,7 @@
>  #define KVM_HC_MIPS_CONSOLE_OUTPUT	8
>  #define KVM_HC_CLOCK_PAIRING		9
>  #define KVM_HC_SEND_IPI		10
> +#define KVM_HC_PAGE_ENC_STATUS		11
>  
>  /*
>   * hypercalls use architecture specific
>