Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Brijesh Singh <brijesh.singh@amd.com>
To:     x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc:     Brijesh Singh <brijesh.singh@amd.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@suse.de>, "H. Peter Anvin" <hpa@zytor.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@redhat.com>
Subject: [PATCH v3 4/4] x86/kvm: use __decrypted attribute in shared variables
Date:   Wed, 29 Aug 2018 13:24:00 -0500
Message-Id: <1535567040-1370-5-git-send-email-brijesh.singh@amd.com>
In-Reply-To: <1535567040-1370-1-git-send-email-brijesh.singh@amd.com>
References: <1535567040-1370-1-git-send-email-brijesh.singh@amd.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Received-SPF: None (protection.outlook.com: amd.com does not designate
 permitted sender hosts)
SpamDiagnosticOutput: 1:99
SpamDiagnosticMetadata: NSPM
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 29 Aug 2018 18:24:18.5805 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 9b9d506c-300c-4865-fa87-08d60ddca2d4
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR12MB2678
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

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 early during boot.

Recently we added a special .data..decrypted section to hold the shared
variables. This section is mapped with C=0 early during boot. 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: 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: kvm@vger.kernel.org
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
---
 arch/x86/kernel/kvmclock.c | 30 +++++++++++++++++++++++++-----
 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index 1e67646..08f5f8a 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 +268,29 @@ 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);
+
+		/*
+		 * The physical address of per-cpu variable will be shared with
+		 * the hypervisor. Let's clear the C-bit before we assign the
+		 * memory to per_cpu variable.
+		 */
+		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