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

2021-01-26 Thread Jürgen Groß 

On 25.01.21 18:26, Andrew Cooper wrote:

On 25/01/2021 14:00, Juergen Gross wrote:

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 4409306364dc..82948251f57b 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -583,6 +583,14 @@ DEFINE_IDTENTRY_RAW(xenpv_exc_debug)
exc_debug(regs);
  }
  
+#ifdef CONFIG_AMD_MEM_ENCRYPT

+DEFINE_IDTENTRY_RAW(xenpv_exc_vmm_communication)
+{
+   /* This should never happen and there is no way to handle it. */
+   panic("X86_TRAP_VC in Xen PV mode.");


Honestly, exactly the same is true of #VE, #HV and #SX.

What we do in the hypervisor is wire up one handler for all unknown
exceptions (to avoid potential future #DF issues) leading to a panic.
Wouldn't it be better to do this unconditionally, especially as #GP/#NP
doesn't work for PV guests for unregistered callbacks, rather than
fixing up piecewise like this?


I agree it would be better to have a "catch all unknown" handler.

I'll have a try how this would look like.


Juergen



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

2021-01-25 Thread Andrew Cooper 
On 25/01/2021 14:00, Juergen Gross wrote:
> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
> index 4409306364dc..82948251f57b 100644
> --- a/arch/x86/xen/enlighten_pv.c
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -583,6 +583,14 @@ DEFINE_IDTENTRY_RAW(xenpv_exc_debug)
>   exc_debug(regs);
>  }
>  
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +DEFINE_IDTENTRY_RAW(xenpv_exc_vmm_communication)
> +{
> + /* This should never happen and there is no way to handle it. */
> + panic("X86_TRAP_VC in Xen PV mode.");

Honestly, exactly the same is true of #VE, #HV and #SX.

What we do in the hypervisor is wire up one handler for all unknown
exceptions (to avoid potential future #DF issues) leading to a panic. 
Wouldn't it be better to do this unconditionally, especially as #GP/#NP
doesn't work for PV guests for unregistered callbacks, rather than
fixing up piecewise like this?

~Andrew

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

2021-01-25 Thread Juergen Gross 
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: GW 
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:c90040033d38 EFLAGS: 00010202
[5.996313] RAX: 0001 RBX: 82a141d0 RCX: 8222ec38
[6.000312] RDX: 8222ec38 RSI: 0005 RDI: c90040033d40
[6.004313] RBP: 8881003984a0 R08: 0007 R09: 888100398000
[6.008312] R10: 0007 R11: c90040246000 R12: 8884082182a8
[6.012313] R13: 0100 R14: 001d R15: 8881003982d0
[6.016316] FS:  () GS:88840820() 
knlGS:
[6.020313] CS:  e030 DS:  ES:  CR0: 80050033
[6.024313] CR2: c900020ef000 CR3: 0220a000 CR4: 00050660
[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 defining a trap entry for X86_TRAP_VC in Xen pv mode.

Fixes: 0786138c78e793 ("x86/sev-es: Add a Runtime #VC Exception Handler")
Cc:  # v5.10
Signed-off-by: Juergen Gross 
---
 arch/x86/include/asm/idtentry.h |  3 +++
 arch/x86/xen/enlighten_pv.c | 11 +++
 arch/x86/xen/xen-asm.S  |  3 +++
 3 files changed, 17 insertions(+)

diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index 247a60a47331..115a76e77e65 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -609,6 +609,9 @@ DECLARE_IDTENTRY_DF(X86_TRAP_DF,exc_double_fault);
 /* #VC */
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 DECLARE_IDTENTRY_VC(X86_TRAP_VC,   exc_vmm_communication);
+#ifdef CONFIG_XEN_PV
+DECLARE_IDTENTRY_RAW(X86_TRAP_VC,  xenpv_exc_vmm_communication);
+#endif
 #endif
 
 #ifdef CONFIG_XEN_PV
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 4409306364dc..82948251f57b 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -583,6 +583,14 @@ DEFINE_IDTENTRY_RAW(xenpv_exc_debug)
exc_debug(regs);
 }
 
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+DEFINE_IDTENTRY_RAW(xenpv_exc_vmm_communication)
+{
+   /* This should never happen and there is no way to handle it. */
+   panic("X86_TRAP_VC in Xen PV mode.");
+}
+#endif
+
 struct trap_array_entry {
void (*orig)(void);
void (*xen)(void);
@@ -625,6 +633,9 @@ static struct trap_array_entry trap_array[] = {
TRAP_ENTRY(exc_coprocessor_error,   false ),
TRAP_ENTRY(exc_alignment_check, false ),
TRAP_ENTRY(exc_simd_coprocessor_error,  false ),
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+   TRAP_ENTRY_REDIR(exc_vmm_communication, true ),
+#endif
 };
 
 static bool __ref get_trap_addr(void **addr, unsigned int ist)
diff --git a/arch/x86/xen/xen-asm.S b/arch/x86/xen/xen-asm.S
index 1cb0e84b9161..16f4db35de44 100644
--- a/arch/x86/xen/xen-asm.S
+++ b/arch/x86/xen/xen-asm.S
@@ -175,6 +175,9 @@ xen_pv_trap asm_exc_alignment_check
 xen_pv_trap asm_exc_machine_check
 #endif /* CONFIG_X86_MCE */
 xen_pv_trap asm_exc_simd_coprocessor_error
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+xen_pv_trap asm_xenpv_exc_vmm_communication
+#endif /* CONFIG_AMD_MEM_ENCRYPT */
 #ifdef CONFIG_IA32_EMULATION
 xen_pv_trap entry_INT80_compat
 #endif
-- 
2.26.2