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

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Message-ID: <95d6d6e3-21d5-17c3-a0a5-dc0bac6d87ca@amd.com>
Date:   Mon, 30 Mar 2020 11:00:14 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Ashish Kalra <Ashish.Kalra@....com>, pbonzini@...hat.com
Cc:     brijesh.singh@....com, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, joro@...tes.org, bp@...e.de,
        thomas.lendacky@....com, x86@...nel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, rientjes@...gle.com,
        srutherford@...gle.com, luto@...nel.org
Subject: Re: [PATCH v6 14/14] KVM: x86: Add kexec support for SEV Live
 Migration.


On 3/30/20 1:23 AM, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@....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.
>
> Signed-off-by: Ashish Kalra <ashish.kalra@....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 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)) {


In patch 13/14, the KVM_FEATURE_SEV_LIVE_MIGRATION is set
unconditionally and because of that now the below code will be executed
on non-SEV guest. IMO, this feature must be cleared for non-SEV guest to
avoid making unnecessary hypercall's.


> +		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();
>  }