[PATCH v2] x86/xen: avoid warning in Xen pv guest with CONFIG_AMD_MEM_ENCRYPT enabled

Juergen Gross
2021-01-27T09:41:03Z

When booting a kernel which has been built with CONFIG_AMD_MEM_ENCRYPT
enabled as a Xen pv guest a warning is issued for each processor:

[ 5.964347] ------------[ cut here ]------------
[ 5.968314] WARNING: CPU: 0 PID: 1 at /home/gross/linux/head/arch/x86/xen/enlighten_pv.c:660 get_trap_addr+0x59/0x90
[ 5.972321] Modules linked in:
[ 5.976313] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G W 5.11.0-rc5-default #75
[ 5.980313] Hardware name: Dell Inc. OptiPlex 9020/0PC5F7, BIOS A05 12/05/2013
[ 5.984313] RIP: e030:get_trap_addr+0x59/0x90
[ 5.988313] Code: 42 10 83 f0 01 85 f6 74 04 84 c0 75 1d b8 01 00 00 00 c3 48 3d 00 80 83 82 72 08 48 3d 20 81 83 82 72 0c b8 01 00 00 00 eb db <0f> 0b 31 c0 c3 48 2d 00 80 83 82 48 ba 72 1c c7 71 1c c7 71 1c 48
[ 5.992313] RSP: e02b:ffffc90040033d38 EFLAGS: 00010202
[ 5.996313] RAX: 0000000000000001 RBX: ffffffff82a141d0 RCX: ffffffff8222ec38
[ 6.000312] RDX: ffffffff8222ec38 RSI: 0000000000000005 RDI: ffffc90040033d40
[ 6.004313] RBP: ffff8881003984a0 R08: 0000000000000007 R09: ffff888100398000
[ 6.008312] R10: 0000000000000007 R11: ffffc90040246000 R12: ffff8884082182a8
[ 6.012313] R13: 0000000000000100 R14: 000000000000001d R15: ffff8881003982d0
[ 6.016316] FS: 0000000000000000(0000) GS:ffff888408200000(0000) knlGS:0000000000000000
[ 6.020313] CS: e030 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 6.024313] CR2: ffffc900020ef000 CR3: 000000000220a000 CR4: 0000000000050660
[ 6.028314] Call Trace:
[ 6.032313] cvt_gate_to_trap.part.7+0x3f/0x90
[ 6.036313] ? asm_exc_double_fault+0x30/0x30
[ 6.040313] xen_convert_trap_info+0x87/0xd0
[ 6.044313] xen_pv_cpu_up+0x17a/0x450
[ 6.048313] bringup_cpu+0x2b/0xc0
[ 6.052313] ? cpus_read_trylock+0x50/0x50
[ 6.056313] cpuhp_invoke_callback+0x80/0x4c0
[ 6.060313] _cpu_up+0xa7/0x140
[ 6.064313] cpu_up+0x98/0xd0
[ 6.068313] bringup_nonboot_cpus+0x4f/0x60
[ 6.072313] smp_init+0x26/0x79
[ 6.076313] kernel_init_freeable+0x103/0x258
[ 6.080313] ? rest_init+0xd0/0xd0
[ 6.084313] kernel_init+0xa/0x110
[ 6.088313] ret_from_fork+0x1f/0x30
[ 6.092313] ---[ end trace be9ecf17dceeb4f3 ]---

Reason is that there is no Xen pv trap entry for X86_TRAP_VC.

Fix that by adding a generic trap handler for unknown traps and wire all
unknown bare metal handlers to this generic handler, which will just
panic the system in case such a trap will ever happen.

Fixes: 0786138c78e793 ("x86/sev-es: Add a Runtime #VC Exception Handler")
Cc: <stable@vger.kernel.org> # v5.10
Signed-off-by: Juergen Gross <jgross@suse.com>
---
V2:
- use generic handler for unknown traps (Andrew Cooper)
---
arch/x86/include/asm/idtentry.h | 1 +
arch/x86/xen/enlighten_pv.c | 14 +++++++++++++-
arch/x86/xen/xen-asm.S | 1 +
3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index 247a60a47331..f656aabd1545 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -613,6 +613,7 @@ DECLARE_IDTENTRY_VC(X86_TRAP_VC, exc_vmm_communication);

#ifdef CONFIG_XEN_PV
DECLARE_IDTENTRY_XENCB(X86_TRAP_OTHER, exc_xen_hypervisor_callback);
+DECLARE_IDTENTRY_RAW(X86_TRAP_OTHER, exc_xen_unknown_trap);
#endif

/* Device interrupts common/spurious */
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 4409306364dc..ca5ac10fcbf7 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -583,6 +583,12 @@ DEFINE_IDTENTRY_RAW(xenpv_exc_debug)
exc_debug(regs);
}

+DEFINE_IDTENTRY_RAW(exc_xen_unknown_trap)
+{
+ /* This should never happen and there is no way to handle it. */
+ panic("Unknown trap in Xen PV mode.");
+}
+
struct trap_array_entry {
void (*orig)(void);
void (*xen)(void);
@@ -631,6 +637,7 @@ static bool __ref get_trap_addr(void **addr, unsigned int ist)
{
unsigned int nr;
bool ist_okay = false;
+ bool found = false;

/*
* Replace trap handler addresses by Xen specific ones.
@@ -645,6 +652,7 @@ static bool __ref get_trap_addr(void **addr, unsigned int ist)
if (*addr == entry->orig) {
*addr = entry->xen;
ist_okay = entry->ist_okay;
+ found = true;
break;
}
}
@@ -655,9 +663,13 @@ static bool __ref get_trap_addr(void **addr, unsigned int ist)
nr = (*addr - (void *)early_idt_handler_array[0]) /
EARLY_IDT_HANDLER_SIZE;
*addr = (void *)xen_early_idt_handler_array[nr];
+ found = true;
}

- if (WARN_ON(ist != 0 && !ist_okay))
+ if (!found)
+ *addr = (void *)xen_asm_exc_xen_unknown_trap;
+
+ if (WARN_ON(found && ist != 0 && !ist_okay))
return false;

return true;
diff --git a/arch/x86/xen/xen-asm.S b/arch/x86/xen/xen-asm.S
index 1cb0e84b9161..53cf8aa35032 100644
--- a/arch/x86/xen/xen-asm.S
+++ b/arch/x86/xen/xen-asm.S
@@ -178,6 +178,7 @@ xen_pv_trap asm_exc_simd_coprocessor_error
#ifdef CONFIG_IA32_EMULATION
xen_pv_trap entry_INT80_compat
#endif
+xen_pv_trap asm_exc_xen_unknown_trap
xen_pv_trap asm_exc_xen_hypervisor_callback

__INIT
--
2.26.2