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Date: Mon, 13 Jul 2020 14:05:05 +0300
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Mike Rapoport <rppt@...nel.org>
Cc: linux-kernel@...r.kernel.org, Alan Cox <alan@...ux.intel.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Andy Lutomirski <luto@...nel.org>,
Christopher Lameter <cl@...ux.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Idan Yaniv <idan.yaniv@....com>,
James Bottomley <jejb@...ux.ibm.com>,
Matthew Wilcox <willy@...radead.org>,
Peter Zijlstra <peterz@...radead.org>,
"Reshetova, Elena" <elena.reshetova@...el.com>,
Thomas Gleixner <tglx@...utronix.de>,
Tycho Andersen <tycho@...ho.ws>, linux-api@...r.kernel.org,
linux-mm@...ck.org, Mike Rapoport <rppt@...ux.ibm.com>
Subject: Re: [RFC PATCH v2 4/5] mm: secretmem: use PMD-size pages to amortize
direct map fragmentation
On Mon, Jul 06, 2020 at 08:20:50PM +0300, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@...ux.ibm.com>
>
> Removing a PAGE_SIZE page from the direct map every time such page is
> allocated for a secret memory mapping will cause severe fragmentation of
> the direct map. This fragmentation can be reduced by using PMD-size pages
> as a pool for small pages for secret memory mappings.
>
> Add a gen_pool per secretmem inode and lazily populate this pool with
> PMD-size pages.
>
> Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
> ---
> mm/secretmem.c | 107 ++++++++++++++++++++++++++++++++++++++++---------
> 1 file changed, 88 insertions(+), 19 deletions(-)
>
> diff --git a/mm/secretmem.c b/mm/secretmem.c
> index df8f8c958cc2..c6fcf6d76951 100644
> --- a/mm/secretmem.c
> +++ b/mm/secretmem.c
> @@ -5,6 +5,7 @@
> #include <linux/memfd.h>
> #include <linux/printk.h>
> #include <linux/pagemap.h>
> +#include <linux/genalloc.h>
> #include <linux/pseudo_fs.h>
> #include <linux/set_memory.h>
> #include <linux/sched/signal.h>
> @@ -23,24 +24,66 @@
> #define SECRETMEM_UNCACHED 0x2
>
> struct secretmem_ctx {
> + struct gen_pool *pool;
> unsigned int mode;
> };
>
> -static struct page *secretmem_alloc_page(gfp_t gfp)
> +static int secretmem_pool_increase(struct secretmem_ctx *ctx, gfp_t gfp)
> {
> - /*
> - * FIXME: use a cache of large pages to reduce the direct map
> - * fragmentation
> - */
> - return alloc_page(gfp);
> + unsigned long nr_pages = (1 << HPAGE_PMD_ORDER);
> + struct gen_pool *pool = ctx->pool;
> + unsigned long addr;
> + struct page *page;
> + int err;
> +
> + page = alloc_pages(gfp, HPAGE_PMD_ORDER);
> + if (!page)
> + return -ENOMEM;
> +
> + addr = (unsigned long)page_address(page);
> + split_page(page, HPAGE_PMD_ORDER);
> +
> + err = gen_pool_add(pool, addr, HPAGE_PMD_SIZE, NUMA_NO_NODE);
> + if (err) {
> + __free_pages(page, HPAGE_PMD_ORDER);
> + return err;
> + }
> +
> + __kernel_map_pages(page, nr_pages, 0);
It's worth nothing that unlike flush_tlb_kernel_range(),
__kernel_map_pages() only flushed local TLB, so other CPU may still have
access to the page. It's shouldn't be a blocker, but deserve a comment.
> +
> + return 0;
> +}
> +
> +static struct page *secretmem_alloc_page(struct secretmem_ctx *ctx,
> + gfp_t gfp)
> +{
> + struct gen_pool *pool = ctx->pool;
> + unsigned long addr;
> + struct page *page;
> + int err;
> +
> + if (gen_pool_avail(pool) < PAGE_SIZE) {
> + err = secretmem_pool_increase(ctx, gfp);
> + if (err)
> + return NULL;
> + }
> +
> + addr = gen_pool_alloc(pool, PAGE_SIZE);
> + if (!addr)
> + return NULL;
> +
> + page = virt_to_page(addr);
> + get_page(page);
> +
> + return page;
> }
>
> static vm_fault_t secretmem_fault(struct vm_fault *vmf)
> {
> + struct secretmem_ctx *ctx = vmf->vma->vm_file->private_data;
> struct address_space *mapping = vmf->vma->vm_file->f_mapping;
> struct inode *inode = file_inode(vmf->vma->vm_file);
> pgoff_t offset = vmf->pgoff;
> - unsigned long addr;
> struct page *page;
> int ret = 0;
>
> @@ -49,7 +92,7 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf)
>
> page = find_get_entry(mapping, offset);
> if (!page) {
> - page = secretmem_alloc_page(vmf->gfp_mask);
> + page = secretmem_alloc_page(ctx, vmf->gfp_mask);
> if (!page)
> return vmf_error(-ENOMEM);
>
> @@ -57,14 +100,8 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf)
> if (unlikely(ret))
> goto err_put_page;
>
> - ret = set_direct_map_invalid_noflush(page);
> - if (ret)
> - goto err_del_page_cache;
> -
> - addr = (unsigned long)page_address(page);
> - flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
> -
> __SetPageUptodate(page);
> + set_page_private(page, (unsigned long)ctx);
>
> ret = VM_FAULT_LOCKED;
> }
> @@ -72,8 +109,6 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf)
> vmf->page = page;
> return ret;
>
> -err_del_page_cache:
> - delete_from_page_cache(page);
> err_put_page:
> put_page(page);
> return vmf_error(ret);
> @@ -155,7 +190,11 @@ static int secretmem_migratepage(struct address_space *mapping,
>
> static void secretmem_freepage(struct page *page)
> {
> - set_direct_map_default_noflush(page);
> + unsigned long addr = (unsigned long)page_address(page);
> + struct secretmem_ctx *ctx = (struct secretmem_ctx *)page_private(page);
> + struct gen_pool *pool = ctx->pool;
> +
> + gen_pool_free(pool, addr, PAGE_SIZE);
> }
>
> static const struct address_space_operations secretmem_aops = {
> @@ -179,13 +218,18 @@ struct file *secretmem_file_create(const char *name, unsigned int flags)
> if (!ctx)
> goto err_free_inode;
>
> + ctx->pool = gen_pool_create(PAGE_SHIFT, NUMA_NO_NODE);
> + if (!ctx->pool)
> + goto err_free_ctx;
> +
> file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem",
> O_RDWR, &secretmem_fops);
> if (IS_ERR(file))
> - goto err_free_ctx;
> + goto err_free_pool;
>
> mapping_set_unevictable(inode->i_mapping);
>
> + inode->i_private = ctx;
> inode->i_mapping->private_data = ctx;
> inode->i_mapping->a_ops = &secretmem_aops;
>
> @@ -197,6 +241,8 @@ struct file *secretmem_file_create(const char *name, unsigned int flags)
>
> return file;
>
> +err_free_pool:
> + gen_pool_destroy(ctx->pool);
> err_free_ctx:
> kfree(ctx);
> err_free_inode:
> @@ -204,11 +250,34 @@ struct file *secretmem_file_create(const char *name, unsigned int flags)
> return file;
> }
>
> +static void secretmem_cleanup_chunk(struct gen_pool *pool,
> + struct gen_pool_chunk *chunk, void *data)
> +{
> + unsigned long start = chunk->start_addr;
> + unsigned long end = chunk->end_addr;
> + unsigned long nr_pages, addr;
> +
> + nr_pages = (end - start + 1) / PAGE_SIZE;
> + __kernel_map_pages(virt_to_page(start), nr_pages, 1);
> +
> + for (addr = start; addr < end; addr += PAGE_SIZE)
> + put_page(virt_to_page(addr));
> +}
> +
> +static void secretmem_cleanup_pool(struct secretmem_ctx *ctx)
> +{
> + struct gen_pool *pool = ctx->pool;
> +
> + gen_pool_for_each_chunk(pool, secretmem_cleanup_chunk, ctx);
> + gen_pool_destroy(pool);
> +}
> +
> static void secretmem_evict_inode(struct inode *inode)
> {
> struct secretmem_ctx *ctx = inode->i_private;
>
> truncate_inode_pages_final(&inode->i_data);
> + secretmem_cleanup_pool(ctx);
> clear_inode(inode);
> kfree(ctx);
> }
> --
> 2.26.2
>
--
Kirill A. Shutemov
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