Hi Luca,
On 15/05/2024 16:26, Luca Fancellu wrote:
>
>
> From: Penny Zheng
>
> We are doing foreign memory mapping for static shared memory, and
> there is a great possibility that it could be super mapped.
> But today, p2m_put_l3_page could not handle superpages.
s/could/can
>
> This commits implements a new function p2m_put_l2_superpage to handle
> 2MB superpages, specifically for helping put extra references for
> foreign superpages.
>
> Modify relinquish_p2m_mapping as well to take into account preemption
> when type is foreign memory and order is above 9 (2MB).
I don't see the reasoning why we don't handle 1GB super pages. It would be
beneficial
to include such in commit msg as well as in the code.
>
> Signed-off-by: Penny Zheng
> Signed-off-by: Luca Fancellu
> ---
> v2:
> - Do not handle 1GB super page as there might be some issue where
>a lot of calls to put_page(...) might be issued which could lead
>to free memory that is a long operation.
> v1:
> - patch from
> https://patchwork.kernel.org/project/xen-devel/patch/20231206090623.1932275-9-penny.zh...@arm.com/
> ---
> xen/arch/arm/mmu/p2m.c | 57 +-
> 1 file changed, 40 insertions(+), 17 deletions(-)
>
> diff --git a/xen/arch/arm/mmu/p2m.c b/xen/arch/arm/mmu/p2m.c
> index 41fcca011cf4..29fdb3b87dd0 100644
> --- a/xen/arch/arm/mmu/p2m.c
> +++ b/xen/arch/arm/mmu/p2m.c
> @@ -753,17 +753,9 @@ static int p2m_mem_access_radix_set(struct p2m_domain
> *p2m, gfn_t gfn,
> return rc;
> }
>
> -/*
> - * Put any references on the single 4K page referenced by pte.
> - * TODO: Handle superpages, for now we only take special references for leaf
> - * pages (specifically foreign ones, which can't be super mapped today).
> - */
> -static void p2m_put_l3_page(const lpae_t pte)
> +/* Put any references on the single 4K page referenced by mfn. */
> +static void p2m_put_l3_page(mfn_t mfn, p2m_type_t type)
> {
> -mfn_t mfn = lpae_get_mfn(pte);
> -
> -ASSERT(p2m_is_valid(pte));
> -
> /*
> * TODO: Handle other p2m types
> *
> @@ -771,16 +763,44 @@ static void p2m_put_l3_page(const lpae_t pte)
> * flush the TLBs if the page is reallocated before the end of
> * this loop.
> */
> -if ( p2m_is_foreign(pte.p2m.type) )
> +if ( p2m_is_foreign(type) )
> {
> ASSERT(mfn_valid(mfn));
> put_page(mfn_to_page(mfn));
> }
> /* Detect the xenheap page and mark the stored GFN as invalid. */
> -else if ( p2m_is_ram(pte.p2m.type) && is_xen_heap_mfn(mfn) )
> +else if ( p2m_is_ram(type) && is_xen_heap_mfn(mfn) )
> page_set_xenheap_gfn(mfn_to_page(mfn), INVALID_GFN);
> }
>
> +/* Put any references on the superpage referenced by mfn. */
> +static void p2m_put_l2_superpage(mfn_t mfn, p2m_type_t type)
> +{
> +unsigned int i;
> +unsigned int level_order = XEN_PT_LEVEL_ORDER(3);
If we know the third level order is always 0 no matter the page shift, does it
make sense to have this variable?
> +
> +for ( i = 0; i < XEN_PT_LPAE_ENTRIES; i++ )
> +{
> +p2m_put_l3_page(mfn, type);
> +
> +mfn = mfn_add(mfn, 1 << level_order);
> +}
> +}
> +
> +/* Put any references on the page referenced by pte. */
> +static void p2m_put_page(const lpae_t pte, unsigned int level)
> +{
> +mfn_t mfn = lpae_get_mfn(pte);
> +
> +ASSERT(p2m_is_valid(pte));
> +
> +/* We have a second level 2M superpage */
> +if ( p2m_is_superpage(pte, level) && (level == 2) )
> +return p2m_put_l2_superpage(mfn, pte.p2m.type);
> +else if ( level == 3 )
> +return p2m_put_l3_page(mfn, pte.p2m.type);
> +}
> +
> /* Free lpae sub-tree behind an entry */
> static void p2m_free_entry(struct p2m_domain *p2m,
> lpae_t entry, unsigned int level)
> @@ -809,9 +829,10 @@ static void p2m_free_entry(struct p2m_domain *p2m,
> #endif
>
> p2m->stats.mappings[level]--;
> -/* Nothing to do if the entry is a super-page. */
> -if ( level == 3 )
> -p2m_put_l3_page(entry);
> +/* TODO: Currently we don't handle 1GB super-page. */
As a future reader of the code it would be beneficial to say why.
> +if ( level >= 2 )
> +p2m_put_page(entry, level);
> +
> return;
> }
>
> @@ -1558,9 +1579,11 @@ int relinquish_p2m_mapping(struct domain *d)
>
> count++;
> /*
> - * Arbitrarily preempt every 512 iterations.
> + * Arbitrarily preempt every 512 iterations or when type is foreign
> + * mapping and the order is above 9 (2MB).
> */
> -if ( !(count % 512) && hypercall_preempt_check() )
> +if ( (!(count % 512) || (p2m_is_foreign(t) && (order > 9))) &&
Instead of (order > 9), use XEN_PT_LEVEL_ORDER(2)
> + hypercall_preempt_check() )
> {
> rc = -ERESTART;
> break;
> --
> 2.34.1
>
~Michal
