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

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