linux-kernel - [PATCH v5 4/5] x86/kvm: use __decrypted attribute in shared variables

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Date:   Thu,  6 Sep 2018 06:43:01 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...e.de>, "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: [PATCH v5 4/5] x86/kvm: use __decrypted attribute in shared variables

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 are able to access the data. To map the
variables we use kernel_physical_mapping_init() to split the large pages,
but splitting large pages requires allocating a new PMD, which fails now
that kvmclock initialization is 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@....com>
Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
Fixes: 368a540e0232 ("x86/kvmclock: Remove memblock dependency")
Cc: Tom Lendacky <thomas.lendacky@....com>
Cc: kvm@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Borislav Petkov <bp@...e.de>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: linux-kernel@...r.kernel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Sean Christopherson <sean.j.christopherson@...el.com>
Cc: kvm@...r.kernel.org
Cc: "Radim Krčmář" <rkrcmar@...hat.com>
---
 arch/x86/kernel/kvmclock.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index 1e67646..376fd3a 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -61,8 +61,8 @@ 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)
-- 
2.7.4