linux-kernel - Re: [PATCH v13 12/12] x86/kvm: Add guest support for detecting and enabling SEV Live Migration feature.

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Message-ID: <20210421152220.GB14004@ashkalra_ubuntu_server>
Date:   Wed, 21 Apr 2021 15:22:20 +0000
From:   Ashish Kalra <ashish.kalra@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     pbonzini@...hat.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, srutherford@...gle.com,
        seanjc@...gle.com, venu.busireddy@...cle.com,
        brijesh.singh@....com, kexec@...ts.infradead.org
Subject: Re: [PATCH v13 12/12] x86/kvm: Add guest support for detecting and
 enabling SEV Live Migration feature.

On Wed, Apr 21, 2021 at 04:44:02PM +0200, Borislav Petkov wrote:
> On Thu, Apr 15, 2021 at 04:01:16PM +0000, Ashish Kalra wrote:
> > From: Ashish Kalra <ashish.kalra@....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?
> 

Yes, the above mentions to get KVM_FEATURE_CPUID and then check if live
migration feature is supported, i.e.,
kvm_para_has_feature(KVM_FEATURE_SEV_LIVE_MIGRATION). The above comments
are written more generically.

> > 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.
> 
> Then, if you feel bored, you could convert sme_active, sev_active,
> sev_es_active, mem_encrypt_active and whetever else code needs to query
> any aspect of SEV being enabled or not, to that function.
> 

Ok.

> > +void __init check_kvm_sev_migration(void)
> > +{
> > +	if (sev_active() &&
> > +	    kvm_para_has_feature(KVM_FEATURE_SEV_LIVE_MIGRATION)) {
> 
> Save an indentation level:
> 
> 	if (!sev_active() ||
> 	    !kvm_para_has_feature(KVM_FEATURE_SEV_LIVE_MIGRATION))
> 		return;
> 
> > +		unsigned long nr_pages;
> > +		int i;
> > +
> > +		pr_info("KVM enable live migration\n");
> 
> That should be at the end of the function and say:
> 
> 		pr_info("KVM live migration enabled.\n");
> 
> > +		WRITE_ONCE(sev_live_migration_enabled, true);
> 
> Why WRITE_ONCE?
> 

Just to ensure that the sev_live_migration_enabled is set to TRUE before
it is used immediately next in the function.

Thanks,
Ashish

> And that needs to go to the end of the function too.
> 
> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
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