Re: [PATCH] x86: detect use of extended APIC ID for AMD CPUs

Jeremy Fitzhardinge
2009-07-21T16:56:49Z

On 07/21/09 03:36, Bastian Blank wrote:
> On Thu, Jun 04, 2009 at 12:40:16PM +0200, Andreas Herrmann wrote:
>
>> Booting a 32-bit kernel on Magny-Cours results in the following panic
>>
>
> This patch breaks Xen really bad. It uses read_pci_config without
> knowing that there is something accessible. Also read_pci_config does
> not define fault handlers.
>
> | (XEN) traps.c:413:d375 Unhandled general protection fault fault/trap [#13] on VCPU 0 [ec=0000]
> | (XEN) domain_crash_sync called from entry.S
> | (XEN) Domain 375 (vcpu#0) crashed on cpu#1:
> | (XEN) ----[ Xen-3.2-1 x86_64 debug=n Not tainted ]----
> | (XEN) CPU: 1
> | (XEN) RIP: e033:[<ffffffff80401d6b>]
> | (XEN) RFLAGS: 0000000000000282 CONTEXT: guest
> | (XEN) rax: 000000008000c068 rbx: ffffffff80618a40 rcx: 0000000000000068
> | (XEN) rdx: 0000000000000cf8 rsi: 000000000000c000 rdi: 0000000000000000
> | (XEN) rbp: 0000000000000018 rsp: ffffffff80621eb0 r8: ffffffff80621efc
> | (XEN) r9: 00000000ffffffff r10: ffffffff80621ef8 r11: 00000000ffffffff
> | (XEN) r12: ffffffffffffffff r13: ffffffff80621fd8 r14: 0000002040404030
> | (XEN) r15: 00000000015bb600 cr0: 000000008005003b cr4: 00000000000006f0
> | (XEN) cr3: 00000002077be000 cr2: 000000204316b000
> | (XEN) ds: 0000 es: 0000 fs: 0000 gs: 0000 ss: e02b cs: e033
> | (XEN) Guest stack trace from rsp=ffffffff80621eb0:
> | (XEN) 0000000000000068 00000000ffffffff 0000000000000000 ffffffff80401d6b
> | (XEN) 000000010000e030 0000000000010082 ffffffff80621ef0 000000000000e02b
> | (XEN) ffffffff804aeb3a 0000000100000000 0000302800000000 ffffffff805bcb20
> | (XEN) ffffffff80651552 0000000000000000 0000000000000000 0000000000fdfd88
> | (XEN) ffffffff8064e47c 0000000001fb9000 ffffffff80545875 0000000000000800
> | (XEN) 0000000000002c00 ffffffff81fb9000 ffffffff80650026 ffffffff805ca1c0
>
> | ffffffff80401d44 T read_pci_config
> | ffffffff804aeb41 t early_init_amd
>
> I see several ways to fix this:
> - Define fault handlers for *_pci_config
> - Check for Xen
> - Disable early PCI access from Xen if running unpriviledged and check
> that in either in *_pci_config or early_init_amd
>
>

I assume "d375" is a domU. cpu_has_apic should be false, and this code
shouldn't be running if the CPU has no (visible) apic.

Does this work? (Completely untested.)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 28e5f59..e2485b0 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -356,7 +356,7 @@ static void __cpuinit early_init_amd(struct cpuinfo_x86 *c)
#endif
#if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_PCI)
/* check CPU config space for extended APIC ID */
- if (c->x86 >= 0xf) {
+ if (cpu_has_apic && c->x86 >= 0xf) {
unsigned int val;
val = read_pci_config(0, 24, 0, 0x68);
if ((val & ((1 << 17) | (1 << 18))) == ((1 << 17) | (1 << 18)))

J