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

Singh, Brijesh
2019-05-03T14:25:13Z

On 4/26/19 4:39 PM, Lendacky, Thomas wrote:
> 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()?
>

Yes, we can use vmalloc() unconditionally. The bitmap size will be
mostly greater than PAGE_SIZE hence the above is useless anyway.

>> +
>> + 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.

I will fix it in next rev.

>
>> +
>> + 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.
>

Yes agreed. thanks