linux-kernel - Re: [RFC 13/16] x86/kvmclock: Share hvclock memory with the host

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Date:   Mon, 25 May 2020 18:25:27 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     David Rientjes <rientjes@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Will Drewry <wad@...omium.org>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "Kleen, Andi" <andi.kleen@...el.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [RFC 13/16] x86/kvmclock: Share hvclock memory with the host

On Mon, May 25, 2020 at 05:22:10PM +0200, Vitaly Kuznetsov wrote:
> "Kirill A. Shutemov" <kirill@...temov.name> writes:
> 
> > hvclock is shared between the guest and the hypervisor. It has to be
> > accessible by host.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > ---
> >  arch/x86/kernel/kvmclock.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> > index 34b18f6eeb2c..ac6c2abe0d0f 100644
> > --- a/arch/x86/kernel/kvmclock.c
> > +++ b/arch/x86/kernel/kvmclock.c
> > @@ -253,7 +253,7 @@ static void __init kvmclock_init_mem(void)
> >  	 * hvclock is shared between the guest and the hypervisor, must
> >  	 * be mapped decrypted.
> >  	 */
> > -	if (sev_active()) {
> > +	if (sev_active() || kvm_mem_protected()) {
> >  		r = set_memory_decrypted((unsigned long) hvclock_mem,
> >  					 1UL << order);
> >  		if (r) {
> 
> Sorry if I missed something but we have other structures which KVM guest
> share with the host,
> 
> sev_map_percpu_data():
> ...
> 	for_each_possible_cpu(cpu) {
> 		__set_percpu_decrypted(&per_cpu(apf_reason, cpu), sizeof(apf_reason));
> 		__set_percpu_decrypted(&per_cpu(steal_time, cpu), sizeof(steal_time));
> 		__set_percpu_decrypted(&per_cpu(kvm_apic_eoi, cpu), sizeof(kvm_apic_eoi));
> 	}
> ...
> 
> Do you handle them somehow in the patchset? (I'm probably just blind
> failing to see how 'early_set_memory_decrypted()' is wired up)

I don't handle them yet: I've seen the function, but have not modified it.
I want to understand first why it doesn't blow up for me without the
change. Any clues?

-- 
 Kirill A. Shutemov