[RFC PATCH v2 16/32] x86: kvm: Provide support to create Guest and HV shared per-CPU variables
Paolo Bonzini
pbonzini at redhat.com
Thu Mar 16 11:06:44 UTC 2017
On 02/03/2017 16:15, Brijesh Singh wrote:
> Some KVM specific MSR's (steal-time, asyncpf, avic_eio) allocates per-CPU
> variable at compile time and share its physical address with hypervisor.
> It presents a challege when SEV is active in guest OS. When SEV is active,
> guest memory is encrypted with guest key and hypervisor will no longer able
> to modify the guest memory. When SEV is active, we need to clear the
> encryption attribute of shared physical addresses so that both guest and
> hypervisor can access the data.
>
> To solve this problem, I have tried these three options:
>
> 1) Convert the static per-CPU to dynamic per-CPU allocation. When SEV is
> detected then clear the encryption attribute. But while doing so I found
> that per-CPU dynamic allocator was not ready when kvm_guest_cpu_init was
> called.
>
> 2) Since the encryption attributes works on PAGE_SIZE hence add some extra
> padding to 'struct kvm-steal-time' to make it PAGE_SIZE and then at runtime
> clear the encryption attribute of the full PAGE. The downside of this was
> now we need to modify structure which may break the compatibility.
>
> 3) Define a new per-CPU section (.data..percpu.hv_shared) which will be
> used to hold the compile time shared per-CPU variables. When SEV is
> detected we map this section with encryption attribute cleared.
>
> This patch implements #3. It introduces a new DEFINE_PER_CPU_HV_SHAHRED
> macro to create a compile time per-CPU variable. When SEV is detected we
> map the per-CPU variable as decrypted (i.e with encryption attribute cleared).
>
> Signed-off-by: Brijesh Singh <brijesh.singh at amd.com>
Looks good to me.
Paolo
> ---
> arch/x86/kernel/kvm.c | 43 +++++++++++++++++++++++++++++++------
> include/asm-generic/vmlinux.lds.h | 3 +++
> include/linux/percpu-defs.h | 9 ++++++++
> 3 files changed, 48 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 099fcba..706a08e 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -75,8 +75,8 @@ static int parse_no_kvmclock_vsyscall(char *arg)
>
> early_param("no-kvmclock-vsyscall", parse_no_kvmclock_vsyscall);
>
> -static DEFINE_PER_CPU(struct kvm_vcpu_pv_apf_data, apf_reason) __aligned(64);
> -static DEFINE_PER_CPU(struct kvm_steal_time, steal_time) __aligned(64);
> +static DEFINE_PER_CPU_HV_SHARED(struct kvm_vcpu_pv_apf_data, apf_reason) __aligned(64);
> +static DEFINE_PER_CPU_HV_SHARED(struct kvm_steal_time, steal_time) __aligned(64);
> static int has_steal_clock = 0;
>
> /*
> @@ -290,6 +290,22 @@ static void __init paravirt_ops_setup(void)
> #endif
> }
>
> +static int kvm_map_percpu_hv_shared(void *addr, unsigned long size)
> +{
> + /* When SEV is active, the percpu static variables initialized
> + * in data section will contain the encrypted data so we first
> + * need to decrypt it and then map it as decrypted.
> + */
> + if (sev_active()) {
> + unsigned long pa = slow_virt_to_phys(addr);
> +
> + sme_early_decrypt(pa, size);
> + return early_set_memory_decrypted(addr, size);
> + }
> +
> + return 0;
> +}
> +
> static void kvm_register_steal_time(void)
> {
> int cpu = smp_processor_id();
> @@ -298,12 +314,17 @@ static void kvm_register_steal_time(void)
> if (!has_steal_clock)
> return;
>
> + if (kvm_map_percpu_hv_shared(st, sizeof(*st))) {
> + pr_err("kvm-stealtime: failed to map hv_shared percpu\n");
> + return;
> + }
> +
> wrmsrl(MSR_KVM_STEAL_TIME, (slow_virt_to_phys(st) | KVM_MSR_ENABLED));
> pr_info("kvm-stealtime: cpu %d, msr %llx\n",
> cpu, (unsigned long long) slow_virt_to_phys(st));
> }
>
> -static DEFINE_PER_CPU(unsigned long, kvm_apic_eoi) = KVM_PV_EOI_DISABLED;
> +static DEFINE_PER_CPU_HV_SHARED(unsigned long, kvm_apic_eoi) = KVM_PV_EOI_DISABLED;
>
> static notrace void kvm_guest_apic_eoi_write(u32 reg, u32 val)
> {
> @@ -327,25 +348,33 @@ static void kvm_guest_cpu_init(void)
> if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF) && kvmapf) {
> u64 pa = slow_virt_to_phys(this_cpu_ptr(&apf_reason));
>
> + if (kvm_map_percpu_hv_shared(this_cpu_ptr(&apf_reason),
> + sizeof(struct kvm_vcpu_pv_apf_data)))
> + goto skip_asyncpf;
> #ifdef CONFIG_PREEMPT
> pa |= KVM_ASYNC_PF_SEND_ALWAYS;
> #endif
> wrmsrl(MSR_KVM_ASYNC_PF_EN, pa | KVM_ASYNC_PF_ENABLED);
> __this_cpu_write(apf_reason.enabled, 1);
> - printk(KERN_INFO"KVM setup async PF for cpu %d\n",
> - smp_processor_id());
> + printk(KERN_INFO"KVM setup async PF for cpu %d msr %llx\n",
> + smp_processor_id(), pa);
> }
> -
> +skip_asyncpf:
> if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) {
> unsigned long pa;
> /* Size alignment is implied but just to make it explicit. */
> BUILD_BUG_ON(__alignof__(kvm_apic_eoi) < 4);
> + if (kvm_map_percpu_hv_shared(this_cpu_ptr(&kvm_apic_eoi),
> + sizeof(unsigned long)))
> + goto skip_pv_eoi;
> __this_cpu_write(kvm_apic_eoi, 0);
> pa = slow_virt_to_phys(this_cpu_ptr(&kvm_apic_eoi))
> | KVM_MSR_ENABLED;
> wrmsrl(MSR_KVM_PV_EOI_EN, pa);
> + printk(KERN_INFO"KVM setup PV EOI for cpu %d msr %lx\n",
> + smp_processor_id(), pa);
> }
> -
> +skip_pv_eoi:
> if (has_steal_clock)
> kvm_register_steal_time();
> }
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 0968d13..8d29910 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -773,6 +773,9 @@
> . = ALIGN(cacheline); \
> *(.data..percpu) \
> *(.data..percpu..shared_aligned) \
> + . = ALIGN(PAGE_SIZE); \
> + *(.data..percpu..hv_shared) \
> + . = ALIGN(PAGE_SIZE); \
> VMLINUX_SYMBOL(__per_cpu_end) = .;
>
> /**
> diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h
> index 8f16299..5af366e 100644
> --- a/include/linux/percpu-defs.h
> +++ b/include/linux/percpu-defs.h
> @@ -172,6 +172,15 @@
> #define DEFINE_PER_CPU_READ_MOSTLY(type, name) \
> DEFINE_PER_CPU_SECTION(type, name, "..read_mostly")
>
> +/* Declaration/definition used for per-CPU variables that must be shared
> + * between hypervisor and guest OS.
> + */
> +#define DECLARE_PER_CPU_HV_SHARED(type, name) \
> + DECLARE_PER_CPU_SECTION(type, name, "..hv_shared")
> +
> +#define DEFINE_PER_CPU_HV_SHARED(type, name) \
> + DEFINE_PER_CPU_SECTION(type, name, "..hv_shared")
> +
> /*
> * Intermodule exports for per-CPU variables. sparse forgets about
> * address space across EXPORT_SYMBOL(), change EXPORT_SYMBOL() to
>
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