On 16.01.2024 20:25, Elias El Yandouzi wrote:
> --- a/xen/arch/x86/pv/dom0_build.c
> +++ b/xen/arch/x86/pv/dom0_build.c
> @@ -382,6 +382,10 @@ int __init dom0_construct_pv(struct domain *d,
> l3_pgentry_t *l3tab = NULL, *l3start = NULL;
> l2_pgentry_t *l2tab = NULL, *l2start = NULL;
> l1_pgentry_t *l1tab = NULL, *l1start = NULL;
> + mfn_t l4start_mfn = INVALID_MFN;
> + mfn_t l3start_mfn = INVALID_MFN;
> + mfn_t l2start_mfn = INVALID_MFN;
> + mfn_t l1start_mfn = INVALID_MFN;
The reason initializers are needed here is, aiui, the overly large scope
of these variables. For example ...
> @@ -708,22 +712,32 @@ int __init dom0_construct_pv(struct domain *d,
> v->arch.pv.event_callback_cs = FLAT_COMPAT_KERNEL_CS;
> }
>
> +#define UNMAP_MAP_AND_ADVANCE(mfn_var, virt_var, maddr) \
> +do { \
> + unmap_domain_page(virt_var); \
> + mfn_var = maddr_to_mfn(maddr); \
> + maddr += PAGE_SIZE; \
> + virt_var = map_domain_page(mfn_var); \
> +} while ( false )
> +
> if ( !compat )
> {
> maddr_to_page(mpt_alloc)->u.inuse.type_info = PGT_l4_page_table;
> - l4start = l4tab = __va(mpt_alloc); mpt_alloc += PAGE_SIZE;
> + UNMAP_MAP_AND_ADVANCE(l4start_mfn, l4start, mpt_alloc);
> + l4tab = l4start;
> clear_page(l4tab);
> - init_xen_l4_slots(l4tab, _mfn(virt_to_mfn(l4start)),
> - d, INVALID_MFN, true);
> - v->arch.guest_table = pagetable_from_paddr(__pa(l4start));
> + init_xen_l4_slots(l4tab, l4start_mfn, d, INVALID_MFN, true);
> + v->arch.guest_table = pagetable_from_mfn(l4start_mfn);
... looks to be required only here, while ...
> }
> else
> {
> /* Monitor table already created by switch_compat(). */
> - l4start = l4tab = __va(pagetable_get_paddr(v->arch.guest_table));
> + l4start_mfn = pagetable_get_mfn(v->arch.guest_table);
> + l4start = l4tab = map_domain_page(l4start_mfn);
... in principle the use of the variable could be avoided here. Below
from here there's no further use of it.
> @@ -781,30 +797,34 @@ int __init dom0_construct_pv(struct domain *d,
>
> if ( compat )
> {
> - l2_pgentry_t *l2t;
> -
> /* Ensure the first four L3 entries are all populated. */
> for ( i = 0, l3tab = l3start; i < 4; ++i, ++l3tab )
> {
> if ( !l3e_get_intpte(*l3tab) )
> {
> maddr_to_page(mpt_alloc)->u.inuse.type_info =
> PGT_l2_page_table;
> - l2tab = __va(mpt_alloc); mpt_alloc += PAGE_SIZE;
> - clear_page(l2tab);
> - *l3tab = l3e_from_paddr(__pa(l2tab), L3_PROT);
> + UNMAP_MAP_AND_ADVANCE(l2start_mfn, l2start, mpt_alloc);
> + clear_page(l2start);
> + *l3tab = l3e_from_mfn(l2start_mfn, L3_PROT);
> }
The updating of l2start is only conditional here, yet ...
> if ( i == 3 )
> l3e_get_page(*l3tab)->u.inuse.type_info |= PGT_pae_xen_l2;
> }
>
> - l2t = map_l2t_from_l3e(l3start[3]);
> - init_xen_pae_l2_slots(l2t, d);
> - unmap_domain_page(l2t);
> + init_xen_pae_l2_slots(l2start, d);
... here you assume it points at the page referenced by the 3rd L3 entry.
Question is why the original code is being replaced here in the first
place: It was already suitably mapping the page in question.
Jan
