From: Dexuan Cui <decui@xxxxxxxxxxxxx> commit 92e68cc558774de01024c18e8b35cdce4731c910 upstream. When Linux runs as an Isolated VM on Hyper-V, it supports AMD SEV-SNP but it's partially enlightened, i.e. cc_platform_has( CC_ATTR_GUEST_MEM_ENCRYPT) is true but sev_active() is false. Commit 4d96f9109109 per se is good, but with it now kvm_setup_vsyscall_timeinfo() -> kvmclock_init_mem() calls set_memory_decrypted(), and later gets stuck when trying to zere out the pages pointed by 'hvclock_mem', if Linux runs as an Isolated VM on Hyper-V. The cause is that here now the Linux VM should no longer access the original guest physical addrss (GPA); instead the VM should do memremap() and access the original GPA + ms_hyperv.shared_gpa_boundary: see the example code in drivers/hv/connection.c: vmbus_connect() or drivers/hv/ring_buffer.c: hv_ringbuffer_init(). If the VM tries to access the original GPA, it keepts getting injected a fault by Hyper-V and gets stuck there. Here the issue happens only when the VM has >=65 vCPUs, because the global static array hv_clock_boot[] can hold 64 "struct pvclock_vsyscall_time_info" (the sizeof of the struct is 64 bytes), so kvmclock_init_mem() only allocates memory in the case of vCPUs > 64. Since the 'hvclock_mem' pages are only useful when the kvm clock is supported by the underlying hypervisor, fix the issue by returning early when Linux VM runs on Hyper-V, which doesn't support kvm clock. Fixes: 4d96f9109109 ("x86/sev: Replace occurrences of sev_active() with cc_platform_has()") Tested-by: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx> Message-Id: <20220225084600.17817-1-decui@xxxxxxxxxxxxx> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/kernel/kvmclock.c | 3 +++ 1 file changed, 3 insertions(+) --- a/arch/x86/kernel/kvmclock.c +++ b/arch/x86/kernel/kvmclock.c @@ -239,6 +239,9 @@ static void __init kvmclock_init_mem(voi static int __init kvm_setup_vsyscall_timeinfo(void) { + if (!kvm_para_available()) + return 0; + kvmclock_init_mem(); #ifdef CONFIG_X86_64 Patches currently in stable-queue which might be from decui@xxxxxxxxxxxxx are queue-5.16/x86-kvmclock-fix-hyper-v-isolated-vm-s-boot-issue-when-vcpus-64.patch