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Subject[RFC 12/17] x86/xen/64: Clean up SP code in cpu_initialize_context()
Date
I'm removing thread_struct::sp0, and Xen's usage of it is slightly
dubious and unnecessary. Use task_top_of_stack() instead.

While we're at at, reorder the code slightly to make it more obvious
what's going on.

Cc: Juergen Gross <jgross@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/xen/smp_pv.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index 51471408fdd1..ad18988b9cd6 100644
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -13,6 +13,7 @@
* single-threaded.
*/
#include <linux/sched.h>
+#include <linux/sched/task_stack.h>
#include <linux/err.h>
#include <linux/slab.h>
#include <linux/smp.h>
@@ -293,12 +294,19 @@ cpu_initialize_context(unsigned int cpu, struct task_struct *idle)
#endif
memset(&ctxt->fpu_ctxt, 0, sizeof(ctxt->fpu_ctxt));

+ /*
+ * Bring up the CPU in cpu_bringup_and_idle() with the stack
+ * pointing just below where pt_regs would be if it were a normal
+ * kernel entry.
+ */
ctxt->user_regs.eip = (unsigned long)cpu_bringup_and_idle;
ctxt->flags = VGCF_IN_KERNEL;
ctxt->user_regs.eflags = 0x1000; /* IOPL_RING1 */
ctxt->user_regs.ds = __USER_DS;
ctxt->user_regs.es = __USER_DS;
ctxt->user_regs.ss = __KERNEL_DS;
+ ctxt->user_regs.cs = __KERNEL_CS;
+ ctxt->user_regs.esp = task_top_of_stack(idle) - sizeof(struct pt_regs);

xen_copy_trap_info(ctxt->trap_ctxt);

@@ -313,8 +321,13 @@ cpu_initialize_context(unsigned int cpu, struct task_struct *idle)
ctxt->gdt_frames[0] = gdt_mfn;
ctxt->gdt_ents = GDT_ENTRIES;

+ /*
+ * Set SS:SP that Xen will use when entering guest kernel mode
+ * from guest user mode. Subsequent calls to load_sp0() can
+ * change this value.
+ */
ctxt->kernel_ss = __KERNEL_DS;
- ctxt->kernel_sp = idle->thread.sp0;
+ ctxt->kernel_sp = task_top_of_stack(idle);

#ifdef CONFIG_X86_32
ctxt->event_callback_cs = __KERNEL_CS;
@@ -326,10 +339,8 @@ cpu_initialize_context(unsigned int cpu, struct task_struct *idle)
(unsigned long)xen_hypervisor_callback;
ctxt->failsafe_callback_eip =
(unsigned long)xen_failsafe_callback;
- ctxt->user_regs.cs = __KERNEL_CS;
per_cpu(xen_cr3, cpu) = __pa(swapper_pg_dir);

- ctxt->user_regs.esp = idle->thread.sp0 - sizeof(struct pt_regs);
ctxt->ctrlreg[3] = xen_pfn_to_cr3(virt_to_gfn(swapper_pg_dir));
if (HYPERVISOR_vcpu_op(VCPUOP_initialise, xen_vcpu_nr(cpu), ctxt))
BUG();
--
2.13.5
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