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

Steve Rutherford
2020-05-30T02:09:21Z

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
>