Re: [RFC 02/16] x86/kvm: Introduce KVM memory protection feature

Kirill A. Shutemov
2020-05-25T15:15:28Z

On Mon, May 25, 2020 at 04:58:51PM +0200, Vitaly Kuznetsov wrote:
> "Kirill A. Shutemov" <kirill@shutemov.name> writes:
>
> > Provide basic helpers, KVM_FEATURE and a hypercall.
> >
> > Host side doesn't provide the feature yet, so it is a dead code for now.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > ---
> > arch/x86/include/asm/kvm_para.h | 5 +++++
> > arch/x86/include/uapi/asm/kvm_para.h | 3 ++-
> > arch/x86/kernel/kvm.c | 16 ++++++++++++++++
> > include/uapi/linux/kvm_para.h | 3 ++-
> > 4 files changed, 25 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> > index 9b4df6eaa11a..3ce84fc07144 100644
> > --- a/arch/x86/include/asm/kvm_para.h
> > +++ b/arch/x86/include/asm/kvm_para.h
> > @@ -10,11 +10,16 @@ extern void kvmclock_init(void);
> >
> > #ifdef CONFIG_KVM_GUEST
> > bool kvm_check_and_clear_guest_paused(void);
> > +bool kvm_mem_protected(void);
> > #else
> > static inline bool kvm_check_and_clear_guest_paused(void)
> > {
> > return false;
> > }
> > +static inline bool kvm_mem_protected(void)
> > +{
> > + return false;
> > +}
> > #endif /* CONFIG_KVM_GUEST */
> >
> > #define KVM_HYPERCALL \
> > diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
> > index 2a8e0b6b9805..c3b499acc98f 100644
> > --- a/arch/x86/include/uapi/asm/kvm_para.h
> > +++ b/arch/x86/include/uapi/asm/kvm_para.h
> > @@ -28,9 +28,10 @@
> > #define KVM_FEATURE_PV_UNHALT 7
> > #define KVM_FEATURE_PV_TLB_FLUSH 9
> > #define KVM_FEATURE_ASYNC_PF_VMEXIT 10
> > -#define KVM_FEATURE_PV_SEND_IPI 11
> > +#define KVM_FEATURE_PV_SEND_IPI 11
>
> Nit: spurrious change
>

I fixed indentation while there. (Look at the file, not the diff to see
what I mean).

> > #define KVM_FEATURE_POLL_CONTROL 12
> > #define KVM_FEATURE_PV_SCHED_YIELD 13
> > +#define KVM_FEATURE_MEM_PROTECTED 14
> >
> > #define KVM_HINTS_REALTIME 0
> >
> > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> > index 6efe0410fb72..bda761ca0d26 100644
> > --- a/arch/x86/kernel/kvm.c
> > +++ b/arch/x86/kernel/kvm.c
> > @@ -35,6 +35,13 @@
> > #include <asm/tlb.h>
> > #include <asm/cpuidle_haltpoll.h>
> >
> > +static bool mem_protected;
> > +
> > +bool kvm_mem_protected(void)
> > +{
> > + return mem_protected;
> > +}
> > +
>
> Honestly, I don't see a need for kvm_mem_protected(), just rename the
> bool if you need kvm_ prefix :-)

For !CONFIG_KVM_GUEST it would not be a variable. We may want to change it
to static branch or something in the future.

> > static int kvmapf = 1;
> >
> > static int __init parse_no_kvmapf(char *arg)
> > @@ -727,6 +734,15 @@ static void __init kvm_init_platform(void)
> > {
> > kvmclock_init();
> > x86_platform.apic_post_init = kvm_apic_init;
> > +
> > + if (kvm_para_has_feature(KVM_FEATURE_MEM_PROTECTED)) {
> > + if (kvm_hypercall0(KVM_HC_ENABLE_MEM_PROTECTED)) {
> > + pr_err("Failed to enable KVM memory protection\n");
> > + return;
> > + }
> > +
> > + mem_protected = true;
> > + }
> > }
>
> Personally, I'd prefer to do this via setting a bit in a KVM-specific
> MSR instead. The benefit is that the guest doesn't need to remember if
> it enabled the feature or not, it can always read the config msr. May
> come handy for e.g. kexec/kdump.

I think we would need to remember it anyway. Accessing MSR is somewhat
expensive. But, okay, I can rework it MSR if needed.

Note, that we can avoid the enabling algother, if we modify BIOS to deal
with private/shared memory. Currently BIOS get system crash if we enable
the feature from time zero.

> > const __initconst struct hypervisor_x86 x86_hyper_kvm = {
> > diff --git a/include/uapi/linux/kvm_para.h b/include/uapi/linux/kvm_para.h
> > index 8b86609849b9..1a216f32e572 100644
> > --- a/include/uapi/linux/kvm_para.h
> > +++ b/include/uapi/linux/kvm_para.h
> > @@ -27,8 +27,9 @@
> > #define KVM_HC_MIPS_EXIT_VM 7
> > #define KVM_HC_MIPS_CONSOLE_OUTPUT 8
> > #define KVM_HC_CLOCK_PAIRING 9
> > -#define KVM_HC_SEND_IPI 10
> > +#define KVM_HC_SEND_IPI 10
>
> Same spurrious change detected.

The same justification :)

> > #define KVM_HC_SCHED_YIELD 11
> > +#define KVM_HC_ENABLE_MEM_PROTECTED 12
> >
> > /*
> > * hypercalls use architecture specific
>
> --
> Vitaly
>
>

--
Kirill A. Shutemov