[PATCH 3/5] x86/hyperv: Fix hyperv_pcpu_input_arg handling when CPUs go online/offline

[Tim Gardner]

From: Michael Kelley <mikelley at microsoft.com>

BugLink: https://bugs.launchpad.net/bugs/2028286

These commits

a494aef23dfc ("PCI: hv: Replace retarget_msi_interrupt_params with hyperv_pcpu_input_arg")
2c6ba4216844 ("PCI: hv: Enable PCI pass-thru devices in Confidential VMs")

update the Hyper-V virtual PCI driver to use the hyperv_pcpu_input_arg
because that memory will be correctly marked as decrypted or encrypted
for all VM types (CoCo or normal). But problems ensue when CPUs in the
VM go online or offline after virtual PCI devices have been configured.

When a CPU is brought online, the hyperv_pcpu_input_arg for that CPU is
initialized by hv_cpu_init() running under state CPUHP_AP_ONLINE_DYN.
But this state occurs after state CPUHP_AP_IRQ_AFFINITY_ONLINE, which
may call the virtual PCI driver and fault trying to use the as yet
uninitialized hyperv_pcpu_input_arg. A similar problem occurs in a CoCo
VM if the MMIO read and write hypercalls are used from state
CPUHP_AP_IRQ_AFFINITY_ONLINE.

When a CPU is taken offline, IRQs may be reassigned in state
CPUHP_TEARDOWN_CPU. Again, the virtual PCI driver may fault trying to
use the hyperv_pcpu_input_arg that has already been freed by a
higher state.

Fix the onlining problem by adding state CPUHP_AP_HYPERV_ONLINE
immediately after CPUHP_AP_ONLINE_IDLE (similar to CPUHP_AP_KVM_ONLINE)
and before CPUHP_AP_IRQ_AFFINITY_ONLINE. Use this new state for
Hyper-V initialization so that hyperv_pcpu_input_arg is allocated
early enough.

Fix the offlining problem by not freeing hyperv_pcpu_input_arg when
a CPU goes offline. Retain the allocated memory, and reuse it if
the CPU comes back online later.

Signed-off-by: Michael Kelley <mikelley at microsoft.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets at redhat.com>
Acked-by: Borislav Petkov (AMD) <bp at alien8.de>
Reviewed-by: Dexuan Cui <decui at microsoft.com>
Link: https://lore.kernel.org/r/1684862062-51576-1-git-send-email-mikelley@microsoft.com
Signed-off-by: Wei Liu <wei.liu at kernel.org>
(cherry picked from commit 9636be85cc5bdd8b7a7f6a53405cbcc52161c93c)
Signed-off-by: Dexuan Cui <decui at microsoft.com>
(cherry picked from commit f4fe22fc55bc5b72aa2fc39474043d7336e5b994 https://github.com/dcui/linux)
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
---
 arch/x86/hyperv/hv_init.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 400ec1573287..a6ccc041539d 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -541,7 +541,7 @@ void __init hyperv_init(void)
 	}
 
 skip_hypercall_pg_init:
-	cpuhp = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/hyperv_init:online",
+	cpuhp = cpuhp_setup_state(CPUHP_AP_HYPERV_ONLINE, "x86/hyperv_init:online",
 				  hv_cpu_init, hv_cpu_die);
 	if (cpuhp < 0)
 		goto clean_guest_os_id;
-- 
2.34.1