Re: [PATCH v8 17/18] KVM: x86: Add kexec support for SEV Live Migration.

[Steve Rutherford <srutherford@google.com>]

On Tue, May 5, 2020 at 2:21 PM Ashish Kalra <Ashish.Kalra@amd.com> wrote:
>
> From: Ashish Kalra <ashish.kalra@amd.com>
>
> Reset the host's page encryption bitmap related to kernel
> specific page encryption status settings before we load a
> new kernel by kexec. We cannot reset the complete
> page encryption bitmap here as we need to retain the
> UEFI/OVMF firmware specific settings.
>
> The host's page encryption bitmap is maintained for the
> guest to keep the encrypted/decrypted state of the guest pages,
> therefore we need to explicitly mark all shared pages as
> encrypted again before rebooting into the new guest kernel.
>
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> ---
>  arch/x86/kernel/kvm.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 4b29815de873..a8bc30d5b15b 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -35,6 +35,7 @@
>  #include <asm/hypervisor.h>
>  #include <asm/tlb.h>
>  #include <asm/cpuidle_haltpoll.h>
> +#include <asm/e820/api.h>
>
>  static int kvmapf = 1;
>
> @@ -358,6 +359,33 @@ static void kvm_pv_guest_cpu_reboot(void *unused)
>          */
>         if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
>                 wrmsrl(MSR_KVM_PV_EOI_EN, 0);
> +       /*
> +        * Reset the host's page encryption bitmap related to kernel
> +        * specific page encryption status settings before we load a
> +        * new kernel by kexec. NOTE: We cannot reset the complete
> +        * page encryption bitmap here as we need to retain the
> +        * UEFI/OVMF firmware specific settings.
> +        */
> +       if (sev_live_migration_enabled() & (smp_processor_id() == 0)) {
> +               int i;
> +               unsigned long nr_pages;
> +
> +               for (i = 0; i < e820_table->nr_entries; i++) {
> +                       struct e820_entry *entry = &e820_table->entries[i];
> +                       unsigned long start_pfn;
> +                       unsigned long end_pfn;
> +
> +                       if (entry->type != E820_TYPE_RAM)
> +                               continue;
What should the behavior be for other memory types that are not
expected to be mucked with by firmware? Should we avoid resetting the
enc status of pmem/pram pages?

My intuition here is that we should only preserve the enc status of
those bits that are set by the firmware.

> +
> +                       start_pfn = entry->addr >> PAGE_SHIFT;
> +                       end_pfn = (entry->addr + entry->size) >> PAGE_SHIFT;
> +                       nr_pages = DIV_ROUND_UP(entry->size, PAGE_SIZE);
> +
> +                       kvm_sev_hypercall3(KVM_HC_PAGE_ENC_STATUS,
> +                                          entry->addr, nr_pages, 1);
> +               }
> +       }
>         kvm_pv_disable_apf();
>         kvm_disable_steal_time();
>  }
> --
> 2.17.1
>