4.16-stable review patch. If anyone has any objections, please let me know.
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From: "van der Linden, Frank" fllinden@amazon.com
[ Upstream commit d1ecfa9d1f402366b1776fbf84e635678a51414f ]
This patch fixes crashes during boot for HVM guests on older (pre HVM vector callback) Xen versions. Without this, current kernels will always fail to boot on those Xen versions.
Sample stack trace:
BUG: unable to handle kernel paging request at ffffffffff200000 IP: __xen_evtchn_do_upcall+0x1e/0x80 PGD 1e0e067 P4D 1e0e067 PUD 1e10067 PMD 235c067 PTE 0 Oops: 0002 [#1] SMP PTI Modules linked in: CPU: 0 PID: 512 Comm: kworker/u2:0 Not tainted 4.14.33-52.13.amzn1.x86_64 #1 Hardware name: Xen HVM domU, BIOS 3.4.3.amazon 11/11/2016 task: ffff88002531d700 task.stack: ffffc90000480000 RIP: 0010:__xen_evtchn_do_upcall+0x1e/0x80 RSP: 0000:ffff880025403ef0 EFLAGS: 00010046 RAX: ffffffff813cc760 RBX: ffffffffff200000 RCX: ffffc90000483ef0 RDX: ffff880020540a00 RSI: ffff880023c78000 RDI: 000000000000001c RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 R13: ffff880025403f5c R14: 0000000000000000 R15: 0000000000000000 FS: 0000000000000000(0000) GS:ffff880025400000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffffffffff200000 CR3: 0000000001e0a000 CR4: 00000000000006f0 Call Trace: <IRQ> do_hvm_evtchn_intr+0xa/0x10 __handle_irq_event_percpu+0x43/0x1a0 handle_irq_event_percpu+0x20/0x50 handle_irq_event+0x39/0x60 handle_fasteoi_irq+0x80/0x140 handle_irq+0xaf/0x120 do_IRQ+0x41/0xd0 common_interrupt+0x7d/0x7d </IRQ>
During boot, the HYPERVISOR_shared_info page gets remapped to make it work with KASLR. This means that any pointer derived from it needs to be adjusted.
The only value that this applies to is the vcpu_info pointer for VCPU 0. For PV and HVM with the callback vector feature, this gets done via the smp_ops prepare_boot_cpu callback. Older Xen versions do not support the HVM callback vector, so there is no Xen-specific smp_ops set up in that scenario. So, the vcpu_info pointer for VCPU 0 never gets set to the proper value, and the first reference of it will be bad. Fix this by resetting it immediately after the remap.
Signed-off-by: Frank van der Linden fllinden@amazon.com Reviewed-by: Eduardo Valentin eduval@amazon.com Reviewed-by: Alakesh Haloi alakeshh@amazon.com Reviewed-by: Vallish Vaidyeshwara vallish@amazon.com Reviewed-by: Boris Ostrovsky boris.ostrovsky@oracle.com Cc: Juergen Gross jgross@suse.com Cc: Boris Ostrovsky boris.ostrovsky@oracle.com Cc: xen-devel@lists.xenproject.org Signed-off-by: Boris Ostrovsky boris.ostrovsky@oracle.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/xen/enlighten_hvm.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
--- a/arch/x86/xen/enlighten_hvm.c +++ b/arch/x86/xen/enlighten_hvm.c @@ -65,6 +65,19 @@ static void __init xen_hvm_init_mem_mapp { early_memunmap(HYPERVISOR_shared_info, PAGE_SIZE); HYPERVISOR_shared_info = __va(PFN_PHYS(shared_info_pfn)); + + /* + * The virtual address of the shared_info page has changed, so + * the vcpu_info pointer for VCPU 0 is now stale. + * + * The prepare_boot_cpu callback will re-initialize it via + * xen_vcpu_setup, but we can't rely on that to be called for + * old Xen versions (xen_have_vector_callback == 0). + * + * It is, in any case, bad to have a stale vcpu_info pointer + * so reset it now. + */ + xen_vcpu_info_reset(0); }
static void __init init_hvm_pv_info(void)