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Subject[PATCH 2/2] x86/kvm: use __decrypted attribute when declaring shared variables
Date
The following commit:

368a540e0232 (x86/kvmclock: Remove memblock dependency)

caused SEV guest regression. When SEV is active, we map the shared
variables (wall_clock and hv_clock_boot) with C=0 to ensure that both
the guest and the hypervisor is able to access the data. To map the
variables we use kernel_physical_mapping_init() to split the large pages,
but this routine fails to allocate a new page. Before the above commit,
kvmclock initialization was called after memory allocator was available
but now its called very early in the boot process.

Recently we added a special .data..decrypted section to hold the shared
variables. This section is mapped with C=0 very early. Use __decrypted
attribute to put the wall_clock and hv_clock_boot in .data..decrypted
section so that they are mapped with C=0.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Fixes: 368a540e0232 ("x86/kvmclock: Remove memblock dependency")
Cc: stable@vger.kernel.org
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: kvm@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: linux-kernel@vger.kernel.org
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
---
arch/x86/kernel/kvmclock.c | 26 +++++++++++++++++++++-----
1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index 1e67646..ae9188a 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -28,6 +28,7 @@
#include <linux/sched/clock.h>
#include <linux/mm.h>
#include <linux/slab.h>
+#include <linux/set_memory.h>

#include <asm/hypervisor.h>
#include <asm/mem_encrypt.h>
@@ -61,8 +62,8 @@ early_param("no-kvmclock-vsyscall", parse_no_kvmclock_vsyscall);
(PAGE_SIZE / sizeof(struct pvclock_vsyscall_time_info))

static struct pvclock_vsyscall_time_info
- hv_clock_boot[HVC_BOOT_ARRAY_SIZE] __aligned(PAGE_SIZE);
-static struct pvclock_wall_clock wall_clock;
+ hv_clock_boot[HVC_BOOT_ARRAY_SIZE] __decrypted __aligned(PAGE_SIZE);
+static struct pvclock_wall_clock wall_clock __decrypted;
static DEFINE_PER_CPU(struct pvclock_vsyscall_time_info *, hv_clock_per_cpu);

static inline struct pvclock_vcpu_time_info *this_cpu_pvti(void)
@@ -267,10 +268,25 @@ static int kvmclock_setup_percpu(unsigned int cpu)
return 0;

/* Use the static page for the first CPUs, allocate otherwise */
- if (cpu < HVC_BOOT_ARRAY_SIZE)
+ if (cpu < HVC_BOOT_ARRAY_SIZE) {
p = &hv_clock_boot[cpu];
- else
- p = kzalloc(sizeof(*p), GFP_KERNEL);
+ } else {
+ int rc;
+ unsigned int sz = sizeof(*p);
+
+ if (sev_active())
+ sz = PAGE_ALIGN(sz);
+
+ p = kzalloc(sz, GFP_KERNEL);
+
+ /* When SEV is active the hv_clock need to be mapped as decrypted. */
+ if (p && sev_active()) {
+ rc = set_memory_decrypted((unsigned long)p, sz >> PAGE_SHIFT);
+ if (rc)
+ return rc;
+ memset(p, 0, sz);
+ }
+ }

per_cpu(hv_clock_per_cpu, cpu) = p;
return p ? 0 : -ENOMEM;
--
2.7.4
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