linux-kernel - Re: [PATCH] ion_system_heap: support X86 archtecture

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Message-ID: <7aad1995-4bb2-a74e-954f-872ea21a752b@redhat.com>
Date:   Sun, 29 Sep 2019 16:57:08 -0400
From:   Laura Abbott <labbott@...hat.com>
To:     jun.zhang@...el.com, sumit.semwal@...aro.org,
        gregkh@...uxfoundation.org, arve@...roid.com, tkjos@...roid.com,
        maco@...roid.com, joel@...lfernandes.org, christian@...uner.io
Cc:     devel@...verdev.osuosl.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org,
        bo <bo.he@...el.com>, Jie A <jie.a.bai@...el.com>
Subject: Re: [PATCH] ion_system_heap: support X86 archtecture

On 9/29/19 3:28 AM, jun.zhang@...el.com wrote:
> From: zhang jun <jun.zhang@...el.com>
> 
> we see tons of warning like:
> [   45.846872] x86/PAT: NDK MediaCodec_:3753 map pfn RAM range req
> write-combining for [mem 0x1e7a80000-0x1e7a87fff], got write-back
> [   45.848827] x86/PAT: .vorbis.decoder:4088 map pfn RAM range req
> write-combining for [mem 0x1e7a58000-0x1e7a58fff], got write-back
> [   45.848875] x86/PAT: NDK MediaCodec_:3753 map pfn RAM range req
> write-combining for [mem 0x1e7a48000-0x1e7a4ffff], got write-back
> [   45.849403] x86/PAT: .vorbis.decoder:4088 map pfn RAM range
> req write-combining for [mem 0x1e7a70000-0x1e7a70fff], got write-back
> 
> check the kernel Documentation/x86/pat.txt, it says:
> A. Exporting pages to users with remap_pfn_range, io_remap_pfn_range,
> vm_insert_pfn
> Drivers wanting to export some pages to userspace do it by using
> mmap interface and a combination of
> 1) pgprot_noncached()
> 2) io_remap_pfn_range() or remap_pfn_range() or vm_insert_pfn()
> With PAT support, a new API pgprot_writecombine is being added.
> So, drivers can continue to use the above sequence, with either
> pgprot_noncached() or pgprot_writecombine() in step 1, followed by step 2.
> 
> In addition, step 2 internally tracks the region as UC or WC in
> memtype list in order to ensure no conflicting mapping.
> 
> Note that this set of APIs only works with IO (non RAM) regions.
> If driver ants to export a RAM region, it has to do set_memory_uc() or
> set_memory_wc() as step 0 above and also track the usage of those pages
> and use set_memory_wb() before the page is freed to free pool.
> 
> the fix follow the pat document, do set_memory_wc() as step 0 and
> use the set_memory_wb() before the page is freed.
> 

All this work needs to be done on the new dma-buf heap rework and I
don't think it makes sense to put it on the staging version

https://lore.kernel.org/lkml/20190906184712.91980-1-john.stultz@linaro.org/

(I also continue to question the value of uncached buffers, especially on
x86)

> Signed-off-by: he, bo <bo.he@...el.com>
> Signed-off-by: zhang jun <jun.zhang@...el.com>
> Signed-off-by: Bai, Jie A <jie.a.bai@...el.com>
> ---
>   drivers/staging/android/ion/ion_system_heap.c | 28 ++++++++++++++++++-
>   1 file changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/android/ion/ion_system_heap.c b/drivers/staging/android/ion/ion_system_heap.c
> index b83a1d16bd89..d298b8194820 100644
> --- a/drivers/staging/android/ion/ion_system_heap.c
> +++ b/drivers/staging/android/ion/ion_system_heap.c
> @@ -13,6 +13,7 @@
>   #include <linux/scatterlist.h>
>   #include <linux/slab.h>
>   #include <linux/vmalloc.h>
> +#include <asm/set_memory.h>
>   
>   #include "ion.h"
>   
> @@ -134,6 +135,13 @@ static int ion_system_heap_allocate(struct ion_heap *heap,
>   	sg = table->sgl;
>   	list_for_each_entry_safe(page, tmp_page, &pages, lru) {
>   		sg_set_page(sg, page, page_size(page), 0);
> +
> +#ifdef CONFIG_X86
> +	if (!(buffer->flags & ION_FLAG_CACHED))
> +		set_memory_wc((unsigned long)page_address(sg_page(sg)),
> +			      PAGE_ALIGN(sg->length) >> PAGE_SHIFT);
> +#endif
> +
>   		sg = sg_next(sg);
>   		list_del(&page->lru);
>   	}
> @@ -162,8 +170,15 @@ static void ion_system_heap_free(struct ion_buffer *buffer)
>   	if (!(buffer->private_flags & ION_PRIV_FLAG_SHRINKER_FREE))
>   		ion_heap_buffer_zero(buffer);
>   
> -	for_each_sg(table->sgl, sg, table->nents, i)
> +	for_each_sg(table->sgl, sg, table->nents, i) {
> +#ifdef CONFIG_X86
> +		if (!(buffer->flags & ION_FLAG_CACHED))
> +			set_memory_wb((unsigned long)page_address(sg_page(sg)),
> +				      PAGE_ALIGN(sg->length) >> PAGE_SHIFT);
> +#endif
> +
>   		free_buffer_page(sys_heap, buffer, sg_page(sg));
> +	}
>   	sg_free_table(table);
>   	kfree(table);
>   }
> @@ -316,6 +331,12 @@ static int ion_system_contig_heap_allocate(struct ion_heap *heap,
>   
>   	buffer->sg_table = table;
>   
> +#ifdef CONFIG_X86
> +	if (!(buffer->flags & ION_FLAG_CACHED))
> +		set_memory_wc((unsigned long)page_address(page),
> +			      PAGE_ALIGN(len) >> PAGE_SHIFT);
> +#endif
> +
>   	return 0;
>   
>   free_table:
> @@ -334,6 +355,11 @@ static void ion_system_contig_heap_free(struct ion_buffer *buffer)
>   	unsigned long pages = PAGE_ALIGN(buffer->size) >> PAGE_SHIFT;
>   	unsigned long i;
>   
> +#ifdef CONFIG_X86
> +	if (!(buffer->flags & ION_FLAG_CACHED))
> +		set_memory_wb((unsigned long)page_address(page), pages);
> +#endif
> +
>   	for (i = 0; i < pages; i++)
>   		__free_page(page + i);
>   	sg_free_table(table);
>