Re: [PATCH v2 1/6] x86/xpti: avoid copying L4 page table contents when possible

[Juergen Gross <jgross@suse.com>]

On 05/03/18 17:43, Jan Beulich wrote:
>>>> On 02.03.18 at 09:13, <jgross@suse.com> wrote:
>> --- a/xen/arch/x86/mm.c
>> +++ b/xen/arch/x86/mm.c
>> @@ -509,6 +509,8 @@ void make_cr3(struct vcpu *v, mfn_t mfn)
>>  
>>  void write_ptbase(struct vcpu *v)
>>  {
>> +    get_cpu_info()->root_pgt_changed = this_cpu(root_pgt) && is_pv_vcpu(v) &&
>> +                                       !is_pv_32bit_vcpu(v);
> 
> Why is_pv_vcpu() when you already check is_pv_32bit_vcpu()?

I check !is_pv_32bit_vcpu() to catch 64-bit pv-domains only.

> 
>> @@ -3704,18 +3706,22 @@ long do_mmu_update(
>>                          break;
>>                      rc = mod_l4_entry(va, l4e_from_intpte(req.val), mfn,
>>                                        cmd == MMU_PT_UPDATE_PRESERVE_AD, v);
>> -                    /*
>> -                     * No need to sync if all uses of the page can be accounted
>> -                     * to the page lock we hold, its pinned status, and uses on
>> -                     * this (v)CPU.
>> -                     */
>> -                    if ( !rc && !cpu_has_no_xpti &&
>> -                         ((page->u.inuse.type_info & PGT_count_mask) >
>> -                          (1 + !!(page->u.inuse.type_info & PGT_pinned) +
>> -                           (pagetable_get_pfn(curr->arch.guest_table) == mfn) 
>> +
>> -                           (pagetable_get_pfn(curr->arch.guest_table_user) ==
>> -                            mfn))) )
>> -                        sync_guest = true;
>> +                    if ( !rc && !cpu_has_no_xpti )
>> +                    {
>> +                        get_cpu_info()->root_pgt_changed = true;
> 
> Why would you set this when a foreign domain's L4 got updated?

Right. I should set it only when modifying the currently active L4.

> And don't you need to disallow updating L4s of running guests now
> (which is a bad idea anyway)?

Yes, I should do that.

> 
>> --- a/xen/arch/x86/smp.c
>> +++ b/xen/arch/x86/smp.c
>> @@ -207,6 +207,8 @@ void invalidate_interrupt(struct cpu_user_regs *regs)
>>      unsigned int flags = flush_flags;
>>      ack_APIC_irq();
>>      perfc_incr(ipis);
>> +    if ( flags & FLUSH_ROOT_PGTBL )
>> +        get_cpu_info()->root_pgt_changed = true;
> 
> While for the caller in do_mmu_update() you don't need it, for
> full correctness you also want to do this in flush_area_mask()
> for the sender, if it's part of the CPU mask.

Right.


Juergen

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