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    Subject[PATCH v5 4/5] x86/kvm: use __decrypted attribute in shared variables
    Date
    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@amd.com>
    Reviewed-by: Tom Lendacky <thomas.lendacky@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 | 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
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