Re: [PATCH RFC 2/3] x86/xen/time: setup vcpu 0 time info page

[Boris Ostrovsky]

On 01/04/2016 03:41 PM, Joao Martins wrote:
> On 01/04/2016 04:07 PM, Boris Ostrovsky wrote:
> > On 12/28/2015 04:52 PM, Joao Martins wrote:
> >
> > > +
> > > +	size = PAGE_ALIGN(sizeof(struct pvclock_vsyscall_time_info));
> > > +	mem = memblock_alloc(size, PAGE_SIZE);
> > > +	if (!mem)
> > > +		return -ENOMEM;
> > > +
> > > +	ti = __va(mem);
> > > +	memset(ti, 0, size);
> > Can you just use get_zeroed_page()? (struct pvclock_vsyscall_time_info
> > is always less than a page, isn't it?).
> Yeah, I can use get_zeroed_page() (struct pvclock_vsyscall_time_info is always
> less than a page).
>
> Additionally perhaps this region shouldn't be freed if PVCLOCK_TSC_STABLE_BIT
> isn't supported, because otherwise I would end up corrupting data elsewhere
> since the pvti would still be periodically updated by Xen, right?

You could try setting it back to NULL. e.g.
    if (!HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_time_memory_area, cpu, 
NULL))
        free_page(..);

-boris
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