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Date: Fri, 3 Apr 2020 01:57:48 +0000
From: Ashish Kalra <ashish.kalra@....com>
To: Krish Sadhukhan <krish.sadhukhan@...cle.com>
Cc: pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com,
hpa@...or.com, joro@...tes.org, bp@...e.de,
thomas.lendacky@....com, x86@...nel.org, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, rientjes@...gle.com,
srutherford@...gle.com, luto@...nel.org, brijesh.singh@....com
Subject: Re: [PATCH v6 08/14] KVM: X86: Introduce KVM_HC_PAGE_ENC_STATUS
hypercall
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@....com>
> >
> > 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@...utronix.de>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: "H. Peter Anvin" <hpa@...or.com>
> > Cc: Paolo Bonzini <pbonzini@...hat.com>
> > Cc: "Radim Krčmář" <rkrcmar@...hat.com>
> > Cc: Joerg Roedel <joro@...tes.org>
> > Cc: Borislav Petkov <bp@...e.de>
> > Cc: Tom Lendacky <thomas.lendacky@....com>
> > Cc: x86@...nel.org
> > Cc: kvm@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org
> > Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> > Signed-off-by: Ashish Kalra <ashish.kalra@....com>
> > ---
> > 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.
> > + 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 ?
>
> ...
>
> .mem_enc_unreg_region
>
> + .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
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