[RFC,13/16] x86/kvmclock: Share hvclock memory with the host
diff mbox series

Message ID 20200522125214.31348-14-kirill.shutemov@linux.intel.com
State New
Headers show
Series
  • KVM protected memory extension
Related show

Commit Message

Kirill A. Shutemov May 22, 2020, 12:52 p.m. UTC
hvclock is shared between the guest and the hypervisor. It has to be
accessible by host.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/kernel/kvmclock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Vitaly Kuznetsov May 25, 2020, 3:22 p.m. UTC | #1
"Kirill A. Shutemov" <kirill@shutemov.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@linux.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)
Kirill A. Shutemov May 25, 2020, 3:25 p.m. UTC | #2
On Mon, May 25, 2020 at 05:22:10PM +0200, Vitaly Kuznetsov wrote:
> "Kirill A. Shutemov" <kirill@shutemov.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@linux.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?
Vitaly Kuznetsov May 25, 2020, 3:42 p.m. UTC | #3
"Kirill A. Shutemov" <kirill@shutemov.name> writes:

> On Mon, May 25, 2020 at 05:22:10PM +0200, Vitaly Kuznetsov wrote:
>> "Kirill A. Shutemov" <kirill@shutemov.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@linux.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?

(if I got the idea of the patchset right) these features are kernel-only
(e.g. QEMU doesn't need to access these areas). E.g. for APF KVM will do
kvm_write_guest_cached() and this will use FOLL_KVM. Guests should not
rely on that and mark all shared areas as unprotected.

Patch
diff mbox series

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) {