[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v3] x86/altp2m: p2m_altp2m_propagate_change() should honor present page order
On Thu, Jan 27, 2022 at 10:07 AM Jan Beulich <jbeulich@xxxxxxxx> wrote: > > For higher order mappings the comparison against p2m->min_remapped_gfn > needs to take the upper bound of the covered GFN range into account, not > just the base GFN. Otherwise, i.e. when dropping a mapping overlapping > the remapped range but the base GFN outside of that range, an altp2m may > wrongly not get reset. > > Note that there's no need to call get_gfn_type_access() ahead of the > check against the remapped range boundaries: None of its outputs are > needed earlier, and p2m_reset_altp2m() doesn't require the lock to be > held. In fact this avoids a latent lock order violation: With per-GFN > locking p2m_reset_altp2m() not only doesn't require the GFN lock to be > held, but holding such a lock would actually not be allowed, as the > function acquires a P2M lock. > > Local variables are moved into the more narrow scope (one is deleted > altogether) to help see their actual life ranges. > > Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx> > --- > Note that this addresses only half of the problem: get_gfn_type_access() > would also need invoking for all of the involved GFNs, not just the 1st > one. > --- > v3: Don't pass the minimum of both orders to p2m_set_entry() (as was the > case in the original code). Restore get_gfn_type_access() return > value checking. > > --- a/xen/arch/x86/mm/p2m.c > +++ b/xen/arch/x86/mm/p2m.c > @@ -2534,9 +2534,6 @@ int p2m_altp2m_propagate_change(struct d > p2m_type_t p2mt, p2m_access_t p2ma) > { > struct p2m_domain *p2m; > - p2m_access_t a; > - p2m_type_t t; > - mfn_t m; > unsigned int i; > unsigned int reset_count = 0; > unsigned int last_reset_idx = ~0; > @@ -2549,15 +2546,16 @@ int p2m_altp2m_propagate_change(struct d > > for ( i = 0; i < MAX_ALTP2M; i++ ) > { > + p2m_type_t t; > + p2m_access_t a; > + > if ( d->arch.altp2m_eptp[i] == mfn_x(INVALID_MFN) ) > continue; > > p2m = d->arch.altp2m_p2m[i]; > - m = get_gfn_type_access(p2m, gfn_x(gfn), &t, &a, 0, NULL); > > /* Check for a dropped page that may impact this altp2m */ > - if ( mfn_eq(mfn, INVALID_MFN) && > - gfn_x(gfn) >= p2m->min_remapped_gfn && > + if ( gfn_x(gfn) + (1UL << page_order) > p2m->min_remapped_gfn && > gfn_x(gfn) <= p2m->max_remapped_gfn ) Why are you dropping the mfn_eq(mfn, INVALID_MFN) check here? Tamas
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