[Part1 PATCH v6 16/17] X86/KVM: Decrypt shared per-cpu variables when SEV is active

[Brijesh Singh]

When SEV is active, guest memory is encrypted with a guest-specific key, a
guest memory region shared with the hypervisor must be mapped as decrypted
before we can share it.

Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: "Radim KrÄmÃÅ" <rkrcmar@xxxxxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: kvm@xxxxxxxxxxxxxxx
Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---

Changes since v5:
early_set_memory_decrypt() takes care of decrypting the memory contents
and changing the C bit hence there is no need to use explicit call
(sme_early_decrypt) to decrypt the memory contents.

Boris,

I removed your R-b since I was not sure if you are okay with the above changes.
please let me know if you are okay with the changes. thanks

 arch/x86/kernel/kvm.c | 35 ++++++++++++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 8bb9594d0761..ff0f04077925 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_DECRYPTED(struct kvm_vcpu_pv_apf_data, apf_reason) __aligned(64);
+static DEFINE_PER_CPU_DECRYPTED(struct kvm_steal_time, steal_time) __aligned(64);
 static int has_steal_clock = 0;
 
 /*
@@ -312,7 +312,7 @@ static void kvm_register_steal_time(void)
 		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_DECRYPTED(unsigned long, kvm_apic_eoi) = KVM_PV_EOI_DISABLED;
 
 static notrace void kvm_guest_apic_eoi_write(u32 reg, u32 val)
 {
@@ -426,9 +426,37 @@ void kvm_disable_steal_time(void)
 	wrmsr(MSR_KVM_STEAL_TIME, 0, 0);
 }
 
+static inline void __set_percpu_decrypted(void *ptr, unsigned long size)
+{
+	early_set_memory_decrypted(slow_virt_to_phys(ptr), size);
+}
+
+/*
+ * Iterate through all possible CPUs and map the memory region pointed
+ * by apf_reason, steal_time and kvm_apic_eoi as decrypted at once.
+ *
+ * Note: we iterate through all possible CPUs to ensure that CPUs
+ * hotplugged will have their per-cpu variable already mapped as
+ * decrypted.
+ */
+static void __init sev_map_percpu_data(void)
+{
+	int cpu;
+
+	if (!sev_active())
+		return;
+
+	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));
+	}
+}
+
 #ifdef CONFIG_SMP
 static void __init kvm_smp_prepare_boot_cpu(void)
 {
+	sev_map_percpu_data();
 	kvm_guest_cpu_init();
 	native_smp_prepare_boot_cpu();
 	kvm_spinlock_init();
@@ -496,6 +524,7 @@ void __init kvm_guest_init(void)
 				      kvm_cpu_online, kvm_cpu_down_prepare) < 0)
 		pr_err("kvm_guest: Failed to install cpu hotplug callbacks\n");
 #else
+	sev_map_percpu_data();
 	kvm_guest_cpu_init();
 #endif
 
-- 
2.9.5