[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v12 1/3] xen/mem_sharing: VM forking
On Wed, Mar 25, 2020 at 04:42:07PM +0000, Julien Grall wrote: > Hi, > > On 25/03/2020 16:34, Tamas K Lengyel wrote: > > > > diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c > > > > index 9f51370327..1ed7d13084 100644 > > > > --- a/xen/arch/x86/mm/p2m.c > > > > +++ b/xen/arch/x86/mm/p2m.c > > > > @@ -509,6 +509,12 @@ mfn_t __get_gfn_type_access(struct p2m_domain > > > > *p2m, unsigned long gfn_l, > > > > > > > > mfn = p2m->get_entry(p2m, gfn, t, a, q, page_order, NULL); > > > > > > > > + /* Check if we need to fork the page */ > > > > + if ( (q & P2M_ALLOC) && p2m_is_hole(*t) && > > > > + !mem_sharing_fork_page(p2m->domain, gfn, q & P2M_UNSHARE) ) > > > > + mfn = p2m->get_entry(p2m, gfn, t, a, q, page_order, NULL); > > > > + > > > > + /* Check if we need to unshare the page */ > > > > if ( (q & P2M_UNSHARE) && p2m_is_shared(*t) ) > > > > { > > > > ASSERT(p2m_is_hostp2m(p2m)); > > > > @@ -588,7 +594,8 @@ struct page_info *p2m_get_page_from_gfn( > > > > return page; > > > > > > > > /* Error path: not a suitable GFN at all */ > > > > - if ( !p2m_is_ram(*t) && !p2m_is_paging(*t) && !p2m_is_pod(*t) ) > > > > + if ( !p2m_is_ram(*t) && !p2m_is_paging(*t) && !p2m_is_pod(*t) > > > > && > > > > + !mem_sharing_is_fork(p2m->domain) ) > > > > return NULL; > > > > } > > > > > > > > diff --git a/xen/common/domain.c b/xen/common/domain.c > > > > index b4eb476a9c..62aed53a16 100644 > > > > --- a/xen/common/domain.c > > > > +++ b/xen/common/domain.c > > > > @@ -1270,6 +1270,9 @@ int map_vcpu_info(struct vcpu *v, unsigned long > > > > gfn, unsigned offset) > > > > > > > > v->vcpu_info = new_info; > > > > v->vcpu_info_mfn = page_to_mfn(page); > > > > +#ifdef CONFIG_MEM_SHARING > > > > + v->vcpu_info_offset = offset; > > > > > > There's no need to introduce this field, you can just use v->vcpu_info > > > & ~PAGE_MASK AFAICT. > > > > Just doing what you suggest above results in: > > > > mem_sharing.c:1603:55: error: invalid operands to binary & (have > > ‘vcpu_info_t * const’ {aka ‘union <anonymous> * const’} and ‘long > > int’) > > d_vcpu->vcpu_info & ~PAGE_MASK); > > > > I can of course cast the vcpu_info pointer to (long int), it's just a > > bit ugly. Thoughts? > > FWIW, I will also need the offset for liveupdate. I have used (unsigned > long)v->vcpu_info & ~PAGE_MASK so far but this is not really pretty. I think using: (vaddr_t)v->vcpu_info & ~PAGE_MASK is acceptable, but that would require adding a vaddr_t typedef to x86. Adding a macro to do so would be OK by me, maybe PAGE_OFFSET or some such? > So I am all for either a new field or a macro hiding this uglyness. Macro would be better IMO, as it's redundant to store the offset when we can obtain it from an existing field. Thanks, Roger.
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