On Tue, Mar 02, 2021 at 02:59:42PM +0000, Quentin Perret wrote: > When memory protection is enabled, the hyp code will require a basic > form of memory management in order to allocate and free memory pages at > EL2. This is needed for various use-cases, including the creation of hyp > mappings or the allocation of stage 2 page tables. > > To address these use-case, introduce a simple memory allocator in the > hyp code. The allocator is designed as a conventional 'buddy allocator', > working with a page granularity. It allows to allocate and free > physically contiguous pages from memory 'pools', with a guaranteed order > alignment in the PA space. Each page in a memory pool is associated > with a struct hyp_page which holds the page's metadata, including its > refcount, as well as its current order, hence mimicking the kernel's > buddy system in the GFP infrastructure. The hyp_page metadata are made > accessible through a hyp_vmemmap, following the concept of > SPARSE_VMEMMAP in the kernel. > > Signed-off-by: Quentin Perret <qper...@google.com> > --- > arch/arm64/kvm/hyp/include/nvhe/gfp.h | 55 +++++++ > arch/arm64/kvm/hyp/include/nvhe/memory.h | 28 ++++ > arch/arm64/kvm/hyp/nvhe/Makefile | 2 +- > arch/arm64/kvm/hyp/nvhe/page_alloc.c | 195 +++++++++++++++++++++++ > 4 files changed, 279 insertions(+), 1 deletion(-) > create mode 100644 arch/arm64/kvm/hyp/include/nvhe/gfp.h > create mode 100644 arch/arm64/kvm/hyp/nvhe/page_alloc.c
[...] > +static void __hyp_attach_page(struct hyp_pool *pool, > + struct hyp_page *p) > +{ > + unsigned int order = p->order; > + struct hyp_page *buddy; > + > + memset(hyp_page_to_virt(p), 0, PAGE_SIZE << p->order); > + > + /* > + * Only the first struct hyp_page of a high-order page (otherwise known > + * as the 'head') should have p->order set. The non-head pages should > + * have p->order = HYP_NO_ORDER. Here @p may no longer be the head > + * after coallescing, so make sure to mark it HYP_NO_ORDER proactively. > + */ > + p->order = HYP_NO_ORDER; > + for (; (order + 1) < pool->max_order; order++) { > + buddy = __find_buddy_avail(pool, p, order); > + if (!buddy) > + break; > + > + /* Take the buddy out of its list, and coallesce with @p */ > + list_del_init(&buddy->node); > + buddy->order = HYP_NO_ORDER; > + p = (p < buddy) ? p : buddy; nit: this is min() > + } > + > + /* Mark the new head, and insert it */ > + p->order = order; > + list_add_tail(&p->node, &pool->free_area[order]); > +} > + > +static void hyp_attach_page(struct hyp_page *p) > +{ > + struct hyp_pool *pool = hyp_page_to_pool(p); > + > + hyp_spin_lock(&pool->lock); > + __hyp_attach_page(pool, p); > + hyp_spin_unlock(&pool->lock); > +} > + > +static struct hyp_page *__hyp_extract_page(struct hyp_pool *pool, > + struct hyp_page *p, > + unsigned int order) > +{ > + struct hyp_page *buddy; > + > + list_del_init(&p->node); > + while (p->order > order) { > + /* > + * The buddy of order n - 1 currently has HYP_NO_ORDER as it > + * is covered by a higher-level page (whose head is @p). Use > + * __find_buddy_nocheck() to find it and inject it in the > + * free_list[n - 1], effectively splitting @p in half. > + */ > + p->order--; > + buddy = __find_buddy_nocheck(pool, p, p->order); > + buddy->order = p->order; > + list_add_tail(&buddy->node, &pool->free_area[buddy->order]); > + } > + > + return p; > +} > + > +void hyp_put_page(void *addr) > +{ > + struct hyp_page *p = hyp_virt_to_page(addr); > + > + if (hyp_page_ref_dec_and_test(p)) > + hyp_attach_page(p); > +} > + > +void hyp_get_page(void *addr) > +{ > + struct hyp_page *p = hyp_virt_to_page(addr); > + > + hyp_page_ref_inc(p); > +} > + > +void *hyp_alloc_pages(struct hyp_pool *pool, unsigned int order) > +{ > + unsigned int i = order; > + struct hyp_page *p; > + > + hyp_spin_lock(&pool->lock); > + > + /* Look for a high-enough-order page */ > + while (i < pool->max_order && list_empty(&pool->free_area[i])) > + i++; > + if (i >= pool->max_order) { > + hyp_spin_unlock(&pool->lock); > + return NULL; > + } > + > + /* Extract it from the tree at the right order */ > + p = list_first_entry(&pool->free_area[i], struct hyp_page, node); > + p = __hyp_extract_page(pool, p, order); > + > + hyp_spin_unlock(&pool->lock); > + hyp_page_ref_inc(p); I find this a little scary, as we momentarily drop the lock. It think it's ok because the reference count on the page must be 0 at this point, but actually then I think it would be clearer to have a hyp_page_ref_init() function which could take the lock, check that the refcount is indeed 0 and then set it to 1. What do you think? Will