Re: [PATCH v3 2/9] x86/PV: properly set shadow allocation for Dom0

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 21/09/2021 08:17, Jan Beulich wrote:
> Leaving shadow setup just to the L1TF tasklet means running Dom0 on a
> minimally acceptable shadow memory pool, rather than what normally
> would be used (also, for example, for PVH). Populate the pool before
> triggering the tasklet, on a best effort basis (again like done for
> PVH).
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Acked-by: Tim Deegan <tim@xxxxxxx>
> ---
> v2: Latch dom0_paging_pages() result.
>
> --- a/xen/arch/x86/mm/shadow/common.c
> +++ b/xen/arch/x86/mm/shadow/common.c
> @@ -1298,7 +1298,7 @@ int shadow_set_allocation(struct domain
>  {
>      struct page_info *sp;
>  
> -    ASSERT(paging_locked_by_me(d));
> +    ASSERT(paging_locked_by_me(d) || system_state < SYS_STATE_active);
>  
>      if ( pages > 0 )
>      {
> --- a/xen/arch/x86/pv/dom0_build.c
> +++ b/xen/arch/x86/pv/dom0_build.c
> @@ -21,6 +21,7 @@
>  #include <asm/page.h>
>  #include <asm/pv/mm.h>
>  #include <asm/setup.h>
> +#include <asm/shadow.h>
>  
>  /* Allow ring-3 access in long mode as guest cannot use ring 1 ... */
>  #define BASE_PROT (_PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_USER)
> @@ -933,7 +934,18 @@ int __init dom0_construct_pv(struct doma
>  #ifdef CONFIG_SHADOW_PAGING
>      if ( opt_dom0_shadow )
>      {
> +        bool preempted;
> +
>          printk("Switching dom0 to using shadow paging\n");
> +
> +        nr_pt_pages = dom0_paging_pages(d, nr_pages);
> +
> +        do {
> +            preempted = false;
> +            shadow_set_allocation(d, nr_pt_pages, &preempted);
> +            process_pending_softirqs();
> +        } while ( preempted );

This is still broken.

The loop setting the shadow allocation needs to be outside of this
conditional, because it is not related to early activation of the l1tf
tasklet.

~Andrew