[Xen-devel] linux-2.6.18/x86: fix context switch on debug hypervisor after 1183:5e3c342a325e

["Jan Beulich" <JBeulich@xxxxxxxx>]

Looking at anything but the result field of a multicall structure after
issuing the multicall is invalid - the debug hypervisor intentionally
clobbers all other fields.

On i386 also remove some left over debugging code.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/arch/i386/kernel/process-xen.c
+++ b/arch/i386/kernel/process-xen.c
@@ -548,7 +548,7 @@ struct task_struct fastcall * __switch_t
 {
        struct thread_struct *prev = &prev_p->thread,
                                 *next = &next_p->thread;
-       int cpu = smp_processor_id();
+       int cpu = smp_processor_id(), cr0_ts;
 #ifndef CONFIG_X86_NO_TSS
        struct tss_struct *tss = &per_cpu(init_tss, cpu);
 #endif
@@ -575,9 +575,6 @@ struct task_struct fastcall * __switch_t
                mcl->args[0] = 1;
                mcl++;
        }
-#if 0 /* lazy fpu sanity check */
-       else BUG_ON(!(read_cr0() & 8));
-#endif
 
        /*
         * Reload esp0.
@@ -639,11 +636,14 @@ struct task_struct fastcall * __switch_t
        BUG_ON(pdo > _pdo + ARRAY_SIZE(_pdo));
 #endif
        BUG_ON(mcl > _mcl + ARRAY_SIZE(_mcl));
-       if (_mcl->op == __HYPERVISOR_fpu_taskswitch)
+       if (_mcl->op == __HYPERVISOR_fpu_taskswitch) {
                __get_cpu_var(xen_x86_cr0_upd) = X86_CR0_TS;
+               cr0_ts = 1;
+       } else
+               cr0_ts = 0;
        if (unlikely(HYPERVISOR_multicall_check(_mcl, mcl - _mcl, NULL)))
                BUG();
-       if (_mcl->op == __HYPERVISOR_fpu_taskswitch) {
+       if (cr0_ts) {
                __get_cpu_var(xen_x86_cr0) |= X86_CR0_TS;
                xen_clear_cr0_upd();
        }
--- a/arch/x86_64/kernel/process-xen.c
+++ b/arch/x86_64/kernel/process-xen.c
@@ -486,7 +486,7 @@ __switch_to(struct task_struct *prev_p, 
 {
        struct thread_struct *prev = &prev_p->thread,
                                 *next = &next_p->thread;
-       int cpu = smp_processor_id();  
+       int cpu = smp_processor_id(), cr0_ts;
 #ifndef CONFIG_X86_NO_TSS
        struct tss_struct *tss = &per_cpu(init_tss, cpu);
 #endif
@@ -572,11 +572,14 @@ __switch_to(struct task_struct *prev_p, 
        BUG_ON(pdo > _pdo + ARRAY_SIZE(_pdo));
 #endif
        BUG_ON(mcl > _mcl + ARRAY_SIZE(_mcl));
-       if (_mcl->op == __HYPERVISOR_fpu_taskswitch)
+       if (_mcl->op == __HYPERVISOR_fpu_taskswitch) {
                __get_cpu_var(xen_x86_cr0_upd) = X86_CR0_TS;
+               cr0_ts = 1;
+       } else
+               cr0_ts = 0;
        if (unlikely(HYPERVISOR_multicall_check(_mcl, mcl - _mcl, NULL)))
                BUG();
-       if (_mcl->op == __HYPERVISOR_fpu_taskswitch) {
+       if (cr0_ts) {
                __get_cpu_var(xen_x86_cr0) |= X86_CR0_TS;
                xen_clear_cr0_upd();
        }

Attachment: xen-x86-cr0-fix.patch
Description: Text document

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