Re: [Xen-devel] [PATCH V7 2/5] x86/mm: allocate logdirty_ranges for altp2ms

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 11/20/18 11:05 AM, Jan Beulich wrote:
>>>> On 19.11.18 at 18:26, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>> For now, only do allocation/deallocation; keeping them in sync
>> will be done in subsequent patches.
>>
>> Logdirty synchronization will only be done for active altp2ms;
>> so allocate logdirty rangesets (copying the host logdirty
>> rangeset) when an altp2m is activated, and free it when
>> deactivated.
>>
>> Write a helper function to do altp2m activiation (appropriately
>> handling failures). Also, refactor p2m_reset_altp2m() so that it
>> can be used to remove redundant codepaths, fixing the locking
>> while we’re at it.
> 
> Perhaps this should have been a separate patch again, such
> that e.g. ...
> 
>> +static void p2m_reset_altp2m(struct domain *d, unsigned int idx,
>> +                             enum altp2m_reset_type reset_type)
>> +{
>> +    struct p2m_domain *p2m;
>> +
>> +    ASSERT(idx < MAX_ALTP2M);
>> +    p2m = d->arch.altp2m_p2m[idx];
>> +
>> +    p2m_lock(p2m);
>> +
>> +    p2m_flush_table_locked(p2m);
>> +
>> +    if ( reset_type == ALTP2M_DEACTIVATE )
>> +        p2m_free_logdirty(p2m);
>> +
>> +    /* Uninit and reinit ept to force TLB shootdown */
>> +    ept_p2m_uninit(p2m);
>> +    ept_p2m_init(p2m);
>> +
>> +    p2m->min_remapped_gfn = gfn_x(INVALID_GFN);
>> +    p2m->max_remapped_gfn = 0;
> 
> ... the addition of these can be properly associated with either
> part of the change. Looking at the code you remove from e.g.
> p2m_flush_altp2m() it's not part of the refactoring, but of what
> this patch's actual purpose is. But this is guesswork of mine
> without the split and without the addition getting explained,
> not the least because this getting moved here from the original
> instance of the function might also mean that it's part of the
> refactoring, but would then need to be done only in the
> ALTP2M_RESET case.

If you mean that p2m->min_remapped_gfn = gfn_x(INVALID_GFN); and
p2m->max_remapped_gfn = 0; should only happen on the ALTP2M_RESET case,
while that is technically true (and should follow from a verbatim
refactoring), George has pointed out that the assignments are in that
case unnecessary but harmless, and so the conditional is not worth it.

I can add the if and treat the RESET case explicitly if that's required.


Thanks,
Razvan

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