Re: [PATCH v13 12/12] x86/kvm: Add guest support for detecting and enabling SEV Live Migration feature.

Ashish Kalra
2021-04-21T19:19:43Z

To reiterate, in addition to KVM_FEATURE_HC_PAGE_ENC_STATUS, we also need
to add the new KVM_FEATURE_SEV_LIVE_MIGRATION feature for guest to check
for host-side support for SEV live migration.

Or will the guest now check KVM_FEATURE_HC_PAGE_ENC_STATUS in CPUID and
then accordingly set bit0 in MSR_KVM_MIGRATION_CONTROL to enable SEV
live migration ?

Thanks,
Ashish

On Wed, Apr 21, 2021 at 06:48:32PM +0000, Ashish Kalra wrote:
> Hello Paolo,
>
> The earlier patch#10 of SEV live migration patches which is now part of
> the guest interface patches used to define
> KVM_FEATURE_SEV_LIVE_MIGRATION.
>
> So now, will the guest patches need to define this feature ?
>
> Thanks,
> Ashish
>
> On Wed, Apr 21, 2021 at 05:38:45PM +0200, Paolo Bonzini wrote:
> > On 21/04/21 16:44, Borislav Petkov wrote:
> > > On Thu, Apr 15, 2021 at 04:01:16PM +0000, Ashish Kalra wrote:
> > > > From: Ashish Kalra <ashish.kalra@amd.com>
> > > >
> > > > The guest support for detecting and enabling SEV Live migration
> > > > feature uses the following logic :
> > > >
> > > > - kvm_init_plaform() invokes check_kvm_sev_migration() which
> > > > checks if its booted under the EFI
> > > >
> > > > - If not EFI,
> > > >
> > > > i) check for the KVM_FEATURE_CPUID
> > >
> > > Where do you do that?
> > >
> > > $ git grep KVM_FEATURE_CPUID
> > > $
> > >
> > > Do you mean
> > >
> > > kvm_para_has_feature(KVM_FEATURE_SEV_LIVE_MIGRATION)
> > >
> > > per chance?
> >
> > Yep. Or KVM_CPUID_FEATURES perhaps.
> >
> > >
> > > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> > > > index 78bb0fae3982..94ef16d263a7 100644
> > > > --- a/arch/x86/kernel/kvm.c
> > > > +++ b/arch/x86/kernel/kvm.c
> > > > @@ -26,6 +26,7 @@
> > > > #include <linux/kprobes.h>
> > > > #include <linux/nmi.h>
> > > > #include <linux/swait.h>
> > > > +#include <linux/efi.h>
> > > > #include <asm/timer.h>
> > > > #include <asm/cpu.h>
> > > > #include <asm/traps.h>
> > > > @@ -429,6 +430,59 @@ static inline void __set_percpu_decrypted(void *ptr, unsigned long size)
> > > > early_set_memory_decrypted((unsigned long) ptr, size);
> > > > }
> > > > +static int __init setup_kvm_sev_migration(void)
> > >
> > > kvm_init_sev_migration() or so.
> > >
> > > ...
> > >
> > > > @@ -48,6 +50,8 @@ EXPORT_SYMBOL_GPL(sev_enable_key);
> > > > bool sev_enabled __section(".data");
> > > > +bool sev_live_migration_enabled __section(".data");
> > >
> > > Pls add a function called something like:
> > >
> > > bool sev_feature_enabled(enum sev_feature)
> > >
> > > and gets SEV_FEATURE_LIVE_MIGRATION and then use it instead of adding
> > > yet another boolean which contains whether some aspect of SEV has been
> > > enabled or not.
> > >
> > > Then add a
> > >
> > > static enum sev_feature sev_features;
> > >
> > > in mem_encrypt.c and that function above will query that sev_features
> > > enum for set flags.
> >
> > Even better: let's stop callings things SEV/SEV_ES. Long term we want
> > anyway to use things like mem_encrypt_enabled (SEV),
> > guest_instruction_trap_enabled (SEV/ES), etc.
> >
> > For this one we don't need a bool at all, we can simply check whether the
> > pvop points to paravirt_nop. Also keep everything but the BSS handling in
> > arch/x86/kernel/kvm.c. Only the BSS handling should be in
> > arch/x86/mm/mem_encrypt.c. This way all KVM paravirt hypercalls and MSRs
> > are in kvm.c.
> >
> > That is:
> >
> > void kvm_init_platform(void)
> > {
> > if (sev_active() &&
> > kvm_para_has_feature(KVM_FEATURE_SEV_LIVE_MIGRATION)) {
> > pv_ops.mmu.notify_page_enc_status_changed =
> > kvm_sev_hc_page_enc_status;
> > /* this takes care of bss_decrypted */
> > early_set_page_enc_status();
> > if (!efi_enabled(EFI_BOOT))
> > wrmsrl(MSR_KVM_SEV_LIVE_MIGRATION,
> > KVM_SEV_LIVE_MIGRATION_ENABLED);
> > }
> > /* existing kvm_init_platform code goes here */
> > }
> >
> > // the pvop is changed to take the pfn, so that the vaddr loop
> > // is not KVM specific
> > static inline void notify_page_enc_status_changed(unsigned long pfn,
> > int npages, bool enc)
> > {
> > PVOP_VCALL3(mmu.page_encryption_changed, pfn, npages, enc);
> > }
> >
> > static void notify_addr_enc_status_changed(unsigned long addr,
> > int numpages, bool enc)
> > {
> > #ifdef CONFIG_PARAVIRT
> > if (pv_ops.mmu.notify_page_enc_status_changed == paravirt_nop)
> > return;
> >
> > /* the body of set_memory_enc_dec_hypercall goes here */
> > for (; vaddr < vaddr_end; vaddr = vaddr_next) {
> > ...
> > notify_page_enc_status_changed(pfn, psize >> PAGE_SHIFT,
> > enc);
> > vaddr_next = (vaddr & pmask) + psize;
> > }
> > #endif
> > }
> >
> > static int __set_memory_enc_dec(unsigned long addr,
> > int numpages, bool enc)
> > {
> > ...
> > cpa_flush(&cpa, 0);
> > notify_addr_enc_status_changed(addr, numpages, enc);
> > return ret;
> > }
> >
> >
> > > +static int __init setup_kvm_sev_migration(void)
> >
> > Please rename this to include efi in the function name.
> >
> > >
> > > + */
> > > + if (!efi_enabled(EFI_BOOT))
> > > + wrmsrl(MSR_KVM_SEV_LIVE_MIGRATION,
> > > + KVM_SEV_LIVE_MIGRATION_ENABLED);
> > > + } else {
> > > + pr_info("KVM enable live migration feature unsupported\n");
> > > + }
> > > +}
> >
> > I think this pr_info is incorrect, because it can still be enabled in the
> > late_initcall. Just remove it as in the sketch above.
> >
> > Paolo
> >