Hi,
You (jeremy) said:
> I've been fighting random crashes in the paravirt tree for a while. 
> After a fair amount of head-banging, it looks to me like the shadow2 
> code is trashing the guest stack (and maybe register state) at random 
> points.
 I have a question about shadow2 in another point of view.
 I've been porting PV-on-HVM driver for ia64 platform. In my jobs,
I had a doubt that shadow2 might occur a problem of memory corruption.
 At first, I had found the problem as a hypervisor crash during
destruction of HVM domain with active VNIF on ia64 platform. The
reason of crash was that hypervisor detected P2M table used by 
gnttab_copy in the HVM domain destruction. Thus I looked for a way
to avoid hypervisor crash in x86 code.
 So, I found that:
 * Before shadow2 age, x86 and ia64 use same logic for domain
 destruction.
 - at first, release gnttab references
 - destruct page table for VCPU
 - destruct P2M table for domain
 - relinquish memory for domain
 * After shadow2 age, x86 introduces delayed P2M table destruction.
 - release gnttab references
 - destruct page table for VCPU
 - relinquish memory for domain
 - destruct P2M table for domain in domain_destroy()
 *** I don't have confidence in my investigation. 
 *** Am I right ?
 I try to show the code that...
[common/domain.c]
 203 void domain_kill(struct domain *d)
 204 {
 205 domain_pause(d);
 206
 207 if ( test_and_set_bit(_DOMF_dying, &d->domain_flags) )
 208 return;
 209
 210 gnttab_release_mappings(d);
 211 domain_relinquish_resources(d);
 212 put_domain(d);
 213
 214 send_guest_global_virq(dom0, VIRQ_DOM_EXC);
 215 }
[arch/x86/domain.c]
 930 void domain_relinquish_resources(struct domain *d)
 931 {
 932 struct vcpu *v;
 933 unsigned long pfn;
 ....
 937 /* Drop the in-use references to page-table bases. */
 938 for_each_vcpu ( d, v )
 ....
 979 /* Relinquish every page of memory. */
 980 relinquish_memory(d, &d->xenpage_list);
 981 relinquish_memory(d, &d->page_list);
 ....
 This is the code for domain_kill phase. I think that hypervisor
relinquishes memory for domain in this code.
 In the other hand...
[common/domain.c]
 322 /* Release resources belonging to task @p. */
 323 void domain_destroy(struct domain *d)
 324 {
 325 struct domain **pd;
 326 atomic_t old, new;
 ....
 354 arch_domain_destroy(d);
 355
 356 free_domain(d);
 357
 358 send_guest_global_virq(dom0, VIRQ_DOM_EXC);
 359 }
[arch/x86/domain.c]
 237 void arch_domain_destroy(struct domain *d)
 238 {
 239 shadow_final_teardown(d);
 ....
[arch/x86/mm/shadow/common.c]
 2580 void shadow_final_teardown(struct domain *d)
 2581 /* Called by arch_domain_destroy(), when it's safe to pull down the p2m
map. */
 2582 {
 ....
 2597 /* It is now safe to pull down the p2m map. */
 2598 if ( d->arch.shadow.p2m_pages != 0 )
 2599 shadow_p2m_teardown(d);
 In this code, P2M table are released.
 If my speculation is correct, shadow2 may occur a problem of memory
corruption.
 What do you think about this point ?
Thanks,
- Tsunehisa Doi
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