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

Ashish Kalra
2021-04-21T18:48:50Z

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
>