Re: [PATCH v6 07/11] arm64/mm, xpfo: temporarily map dcache regions

Mark Rutland
2017-09-14T18:25:59Z

On Thu, Sep 07, 2017 at 11:36:05AM -0600, Tycho Andersen wrote:
> From: Juerg Haefliger <juerg.haefliger@canonical.com>
>
> If the page is unmapped by XPFO, a data cache flush results in a fatal
> page fault, so let's temporarily map the region, flush the cache, and then
> unmap it.
>
> v6: actually flush in the face of xpfo, and temporarily map the underlying
> memory so it can be flushed correctly
>
> CC: linux-arm-kernel@lists.infradead.org
> Signed-off-by: Juerg Haefliger <juerg.haefliger@canonical.com>
> Signed-off-by: Tycho Andersen <tycho@docker.com>
> ---
> arch/arm64/mm/flush.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
> index 21a8d828cbf4..e335e3fd4fca 100644
> --- a/arch/arm64/mm/flush.c
> +++ b/arch/arm64/mm/flush.c
> @@ -20,6 +20,7 @@
> #include <linux/export.h>
> #include <linux/mm.h>
> #include <linux/pagemap.h>
> +#include <linux/xpfo.h>
>
> #include <asm/cacheflush.h>
> #include <asm/cache.h>
> @@ -28,9 +29,15 @@
> void sync_icache_aliases(void *kaddr, unsigned long len)
> {
> unsigned long addr = (unsigned long)kaddr;
> + unsigned long num_pages = XPFO_NUM_PAGES(addr, len);
> + void *mapping[num_pages];
>
> if (icache_is_aliasing()) {
> + xpfo_temp_map(kaddr, len, mapping,
> + sizeof(mapping[0]) * num_pages);
> __clean_dcache_area_pou(kaddr, len);
> + xpfo_temp_unmap(kaddr, len, mapping,
> + sizeof(mapping[0]) * num_pages);

Does this create the mapping in-place?

Can we not just kmap_atomic() an alias? Or is there a problem with that?

Thanks,
Mark.