Re: [PATCH v6 14/14] KVM: x86: Add kexec support for SEV Live Migration.

[Krish Sadhukhan]

On 4/4/20 2:57 PM, Ashish Kalra wrote:
> 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.
>
> On Fri, Apr 03, 2020 at 05:55:52PM -0700, Krish Sadhukhan wrote:
> > On 3/29/20 11:23 PM, Ashish Kalra wrote:
> > > From: Ashish Kalra <ashish.kalra@xxxxxxx>
> > >
> > > 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.
> >
> > Can the commit message mention why host page encryption needs to be reset ?
> > Since the theme of these patches is guest migration in-SEV context, it might
> > be useful to mention why the host context comes in here.
> >
> > > Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> > > ---
> > >    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 8fcee0b45231..ba6cce3c84af 100644
> > > --- a/arch/x86/kernel/kvm.c
> > > +++ b/arch/x86/kernel/kvm.c
> > > @@ -34,6 +34,7 @@
> > >    #include <asm/hypervisor.h>
> > >    #include <asm/tlb.h>
> > >    #include <asm/cpuidle_haltpoll.h>
> > > +#include <asm/e820/api.h>
> > >    static int kvmapf = 1;
> > > @@ -357,6 +358,33 @@ 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 (kvm_para_has_feature(KVM_FEATURE_SEV_LIVE_MIGRATION) &&
> > > +		(smp_processor_id() == 0)) {
> > > +		unsigned long nr_pages;
> > > +		int i;
> > > +
> > > +		for (i = 0; i < e820_table->nr_entries; i++) {
> > > +			struct e820_entry *entry = &e820_table->entries[i];
> > > +			unsigned long start_pfn, end_pfn;
> > > +
> > > +			if (entry->type != E820_TYPE_RAM)
> > > +				continue;
> > > +
> > > +			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();
> > >    }

Thanks for the explanation. It will certainly help one understand the 
context better if you add it to the commit message.

Reviewed-by: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx>