On 06.01.2025 12:26, Andrew Cooper wrote:
> Regular data access into the trampoline is via the directmap.
>
> As now discussed quite extensively in asm/trampoline.h, the trampoline is
> arranged so that only the AP and S3 paths need an identity mapping, and that
> they fit within a single page.
>
> Right now, PFN_UP(trampoline_end - trampoline_start) is 2, causing more than
> expected of the trampoline to be mapped. Cut it down just the single page it
> ought to be.
>
> Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
Acked-by: Jan Beulich <jbeul...@suse.com>
on the basis that this improves things. However, ...
> --- a/xen/arch/x86/x86_64/mm.c
> +++ b/xen/arch/x86/x86_64/mm.c
> @@ -718,14 +718,16 @@ void __init zap_low_mappings(void)
> {
> BUG_ON(num_online_cpus() != 1);
>
> - /* Remove aliased mapping of first 1:1 PML4 entry. */
> + /* Stop using l?_bootmap[] mappings. */
> l4e_write(&idle_pg_table[0], l4e_empty());
> flush_local(FLUSH_TLB_GLOBAL);
>
> - /* Replace with mapping of the boot trampoline only. */
> + /*
> + * Insert an identity mapping of the AP/S3 part of the trampoline, which
> + * is arranged to fit in a single page.
> + */
> map_pages_to_xen(trampoline_phys, maddr_to_mfn(trampoline_phys),
> - PFN_UP(trampoline_end - trampoline_start),
> - __PAGE_HYPERVISOR_RX);
> + 1, __PAGE_HYPERVISOR_RX);
... literal numbers like this - however well they are commented - are
potentially problematic to locate in case something changes significantly.
The 1 here really would want connecting with the .equ establishing
wakeup_stack.
Jan
