Re: [Xen-devel] [v2 06/11] vmx: add help functions to support PML

[Kai Huang <kai.huang@xxxxxxxxxxxxxxx>]

On 04/17/2015 02:23 PM, Jan Beulich wrote:
> > > > On 17.04.15 at 05:10, <kai.huang@xxxxxxxxxxxxxxx> wrote:
> > On 04/16/2015 11:42 PM, Jan Beulich wrote:
> > > > > > On 15.04.15 at 09:03, <kai.huang@xxxxxxxxxxxxxxx> wrote:
> > > > +void vmx_vcpu_flush_pml_buffer(struct vcpu *v)
> > > > +{
> > > > +    uint64_t *pml_buf;
> > > > +    unsigned long pml_idx;
> > > > +
> > > > +    ASSERT(vmx_vcpu_pml_enabled(v));
> > > > +
> > > > +    vmx_vmcs_enter(v);
> > > > +
> > > > +    __vmread(GUEST_PML_INDEX, &pml_idx);
> > > Don't you require the vCPU to be non-running or current when you
> > > get here? If so, perhaps add a respective ASSERT()?
> > Yes an ASSERT would be better.
> >
> > v->pause_count will be increased if vcpu is kicked out by domain_pause
> > explicitly, but looks the same thing won't be done if vcpu is kicked out
> > by PML buffer full VMEXIT. So should the ASSERT be done like below?
> >
> > ASSERT(atomic_read(&v->pause_count) || (v == current));
> For one I'd reverse the two parts. And then I think pause count
> being non-zero is not a sufficient condition - if a non-synchronous
> pause was issued against the vCPU it may still be running. I'd
> suggest !vcpu_runnable(v) && !v->is_running, possibly with the
> pause count check instead of the runnable one if the only
> permitted case where v != current requires the vCPU to be
> paused.
The vmx_vcpu_flush_pml_buffer is only supposed to be called in below cases:

    - When PML full VMEXIT happens
    - In paging_log_dirty_op & hap_track_dirty_vram, before reporting 
dirty pages to userspace.
    - In vmx_vcpu_disable_pml, called from vmx_vcpu_destroy, or when 
log-dirty mode is disabled.
In the latter two cases, domain_pause is guaranteed to be called before 
vmx_vcpu_flush_pml_buffer is called, therefore looks there's no 
possibility of non-synchronous pause of the vcpu.
Or are you suggesting we should suppose this function can be called from 
any caller, and meanwhile is able to act reasonably?
> > > > +        /*
> > > > +         * Need to change type from log-dirty to normal memory for logged GFN.
> > > > +         * hap_track_dirty_vram depends on it to work. And we really only need
> > > > +         * to mark GFNs which hve been successfully changed from log-dirty to
> > > > +         * normal memory to be dirty.
> > > > +         */
> > > > +        if ( !p2m_change_type_one(v->domain, gfn, p2m_ram_logdirty,
> > > > +                    p2m_ram_rw) )
> > > Indentation.
> > To be where exactly? Sorry I didn't find an example to refer in such case.
> p2m_ram_rw should align with the v in v->domain.
Understood. Will do.

Thanks,
-Kai
> Jan

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