On Tue, Sep 10, 2024 at 11:00:27AM +0200, Jan Beulich wrote: > On 10.09.2024 10:54, Roger Pau Monné wrote: > > On Tue, Aug 13, 2024 at 05:54:54PM +0200, Jan Beulich wrote: > >> On 26.07.2024 17:21, Roger Pau Monne wrote: > >>> The idle_pg_table L4 is cloned to create all the other L4 Xen uses, and > >>> hence > >>> it shouldn't be modified once further L4 are created. > >> > >> Yes, but the window between moving into SYS_STATE_smp_boot and Dom0 having > >> its initial page tables created is quite large. If the justification was > >> relative to AP bringup, that may be all fine. But when related to cloning, > >> I think that would then truly want keying to there being any non-system > >> domain(s). > > > > Further changes in this series will add a per-CPU idle page table, and > > hence we need to ensure that by the time APs are started the BSP L4 idle > > page directory is not changed, as otherwise the copies in the APs > > would get out of sync. > > > > The idle system domain is indeed tied to the idle page talbes, but the > > idle vCPU0 (the BSP) directly uses idle_pg_table (no copying), and > > hence it's fine to allow modifications of the L4 idle page table > > directory up to when APs are started (those will indeed make copies of > > the idle L4. > > Which may want at least mentioning in the description then. I take it > that ... > > >>> --- a/xen/arch/x86/mm.c > >>> +++ b/xen/arch/x86/mm.c > >>> @@ -5023,6 +5023,12 @@ static l3_pgentry_t *virt_to_xen_l3e(unsigned long > >>> v) > >>> mfn_t l3mfn; > >>> l3_pgentry_t *l3t = alloc_mapped_pagetable(&l3mfn); > >>> > >>> + /* > >>> + * dom0 is build at smp_boot, at which point we already create > >>> new L4s > >>> + * based on idle_pg_table. > >>> + */ > > ... this comment is then refined by the later patches you refer to?
Hm, I would have to double check, not sure I've updated it once the idle_pg_table is cloned for AP bringup. Will expand commit message and update the comment here if not done already by later patches. Thanks, Roger.
