Re: [PATCH v2 4/5] ALSA: xen-front: Implement handling of shared buffers

[Oleksandr Andrushchenko <andr2000@gmail.com>]

On 04/16/2018 04:39 PM, Juergen Gross wrote:
> On 16/04/18 08:24, Oleksandr Andrushchenko wrote:
>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>
>> Implement shared buffer handling according to the
>> para-virtualized sound device protocol at xen/interface/io/sndif.h:
>>    - manage buffer memory
>>    - handle granted references
>>    - handle page directories
>>
>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>> ---
>>   sound/xen/Makefile              |   3 +-
>>   sound/xen/xen_snd_front.c       |   8 ++
>>   sound/xen/xen_snd_front_shbuf.c | 193 ++++++++++++++++++++++++++++++++++++++++
>>   sound/xen/xen_snd_front_shbuf.h |  36 ++++++++
>>   4 files changed, 239 insertions(+), 1 deletion(-)
>>   create mode 100644 sound/xen/xen_snd_front_shbuf.c
>>   create mode 100644 sound/xen/xen_snd_front_shbuf.h
>>
>> diff --git a/sound/xen/Makefile b/sound/xen/Makefile
>> index 03c669984000..f028bc30af5d 100644
>> --- a/sound/xen/Makefile
>> +++ b/sound/xen/Makefile
>> @@ -2,6 +2,7 @@
>>   
>>   snd_xen_front-objs := xen_snd_front.o \
>>   		      xen_snd_front_cfg.o \
>> -		      xen_snd_front_evtchnl.o
>> +		      xen_snd_front_evtchnl.o \
>> +		      xen_snd_front_shbuf.o
>>   
>>   obj-$(CONFIG_SND_XEN_FRONTEND) += snd_xen_front.o
>> diff --git a/sound/xen/xen_snd_front.c b/sound/xen/xen_snd_front.c
>> index eb46bf4070f9..0569c6c596a3 100644
>> --- a/sound/xen/xen_snd_front.c
>> +++ b/sound/xen/xen_snd_front.c
>> @@ -11,6 +11,7 @@
>>   #include <linux/delay.h>
>>   #include <linux/module.h>
>>   
>> +#include <xen/page.h>
>>   #include <xen/platform_pci.h>
>>   #include <xen/xen.h>
>>   #include <xen/xenbus.h>
>> @@ -186,6 +187,13 @@ static struct xenbus_driver xen_driver = {
>>   
>>   static int __init xen_drv_init(void)
>>   {
>> +	/* At the moment we only support case with XEN_PAGE_SIZE == PAGE_SIZE */
>> +	if (XEN_PAGE_SIZE != PAGE_SIZE) {
>> +		pr_err(XENSND_DRIVER_NAME ": different kernel and Xen page sizes are not supported: XEN_PAGE_SIZE (%lu) != PAGE_SIZE (%lu)\n",
>> +		       XEN_PAGE_SIZE, PAGE_SIZE);
>> +		return -ENODEV;
>> +	}
> Do you really want to print that error message on bare metal?
will move it down after xen_domain/xen_has_pv_devices checks
>> +
>>   	if (!xen_domain())
>>   		return -ENODEV;
>>   
>> diff --git a/sound/xen/xen_snd_front_shbuf.c b/sound/xen/xen_snd_front_shbuf.c
>> new file mode 100644
>> index 000000000000..6845dbc7fdf5
>> --- /dev/null
>> +++ b/sound/xen/xen_snd_front_shbuf.c
>> @@ -0,0 +1,193 @@
>> +// SPDX-License-Identifier: GPL-2.0 OR MIT
>> +
>> +/*
>> + * Xen para-virtual sound device
>> + *
>> + * Copyright (C) 2016-2018 EPAM Systems Inc.
>> + *
>> + * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>> + */
>> +
>> +#include <xen/xen.h>
>> +#include <xen/xenbus.h>
>> +
>> +#include "xen_snd_front_shbuf.h"
>> +
>> +grant_ref_t xen_snd_front_shbuf_get_dir_start(struct xen_snd_front_shbuf *buf)
>> +{
>> +	if (!buf->grefs)
>> +		return GRANT_INVALID_REF;
>> +
>> +	return buf->grefs[0];
>> +}
>> +
>> +void xen_snd_front_shbuf_clear(struct xen_snd_front_shbuf *buf)
>> +{
>> +	memset(buf, 0, sizeof(*buf));
>> +}
>> +
>> +void xen_snd_front_shbuf_free(struct xen_snd_front_shbuf *buf)
>> +{
>> +	int i;
>> +
>> +	if (buf->grefs) {
>> +		for (i = 0; i < buf->num_grefs; i++)
>> +			if (buf->grefs[i] != GRANT_INVALID_REF)
>> +				gnttab_end_foreign_access(buf->grefs[i],
>> +							  0, 0UL);
>> +		kfree(buf->grefs);
>> +	}
>> +	kfree(buf->directory);
>> +	free_pages_exact(buf->buffer, buf->buffer_sz);
>> +	xen_snd_front_shbuf_clear(buf);
>> +}
>> +
>> +/*
>> + * number of grant references a page can hold with respect to the
>> + * xensnd_page_directory header
>> + */
>> +#define XENSND_NUM_GREFS_PER_PAGE ((XEN_PAGE_SIZE - \
>> +		offsetof(struct xensnd_page_directory, gref)) / \
>> +		sizeof(grant_ref_t))
>> +
>> +static void fill_page_dir(struct xen_snd_front_shbuf *buf,
>> +			  int num_pages_dir)
>> +{
>> +	struct xensnd_page_directory *page_dir;
>> +	unsigned char *ptr;
>> +	int i, cur_gref, grefs_left, to_copy;
>> +
>> +	ptr = buf->directory;
>> +	grefs_left = buf->num_grefs - num_pages_dir;
>> +	/*
>> +	 * skip grant references at the beginning, they are for pages granted
>> +	 * for the page directory itself
>> +	 */
>> +	cur_gref = num_pages_dir;
>> +	for (i = 0; i < num_pages_dir; i++) {
>> +		page_dir = (struct xensnd_page_directory *)ptr;
>> +		if (grefs_left <= XENSND_NUM_GREFS_PER_PAGE) {
>> +			to_copy = grefs_left;
>> +			page_dir->gref_dir_next_page = GRANT_INVALID_REF;
>> +		} else {
>> +			to_copy = XENSND_NUM_GREFS_PER_PAGE;
>> +			page_dir->gref_dir_next_page = buf->grefs[i + 1];
>> +		}
>> +
>> +		memcpy(&page_dir->gref, &buf->grefs[cur_gref],
>> +		       to_copy * sizeof(grant_ref_t));
>> +
>> +		ptr += XEN_PAGE_SIZE;
>> +		grefs_left -= to_copy;
>> +		cur_gref += to_copy;
>> +	}
>> +}
>> +
>> +static int grant_references(struct xenbus_device *xb_dev,
>> +			    struct xen_snd_front_shbuf *buf,
>> +			    int num_pages_dir, int num_pages_buffer,
>> +			    int num_grefs)
>> +{
>> +	grant_ref_t priv_gref_head;
>> +	unsigned long frame;
>> +	int ret, i, j, cur_ref;
>> +	int otherend_id;
>> +
>> +	ret = gnttab_alloc_grant_references(num_grefs, &priv_gref_head);
>> +	if (ret)
>> +		return ret;
>> +
>> +	buf->num_grefs = num_grefs;
>> +	otherend_id = xb_dev->otherend_id;
>> +	j = 0;
>> +
>> +	for (i = 0; i < num_pages_dir; i++) {
>> +		cur_ref = gnttab_claim_grant_reference(&priv_gref_head);
>> +		if (cur_ref < 0) {
>> +			ret = cur_ref;
>> +			goto fail;
>> +		}
>> +
>> +		frame = xen_page_to_gfn(virt_to_page(buf->directory +
>> +						     XEN_PAGE_SIZE * i));
>> +		gnttab_grant_foreign_access_ref(cur_ref, otherend_id, frame, 0);
>> +		buf->grefs[j++] = cur_ref;
>> +	}
>> +
>> +	for (i = 0; i < num_pages_buffer; i++) {
>> +		cur_ref = gnttab_claim_grant_reference(&priv_gref_head);
>> +		if (cur_ref < 0) {
>> +			ret = cur_ref;
>> +			goto fail;
>> +		}
>> +
>> +		frame = xen_page_to_gfn(virt_to_page(buf->buffer +
>> +						     XEN_PAGE_SIZE * i));
>> +		gnttab_grant_foreign_access_ref(cur_ref, otherend_id, frame, 0);
>> +		buf->grefs[j++] = cur_ref;
>> +	}
>> +
>> +	gnttab_free_grant_references(priv_gref_head);
>> +	fill_page_dir(buf, num_pages_dir);
>> +	return 0;
>> +
>> +fail:
>> +	gnttab_free_grant_references(priv_gref_head);
>> +	return ret;
>> +}
>> +
>> +static int alloc_int_buffers(struct xen_snd_front_shbuf *buf,
>> +			     int num_pages_dir, int num_pages_buffer,
>> +			     int num_grefs)
>> +{
>> +	buf->grefs = kcalloc(num_grefs, sizeof(*buf->grefs), GFP_KERNEL);
>> +	if (!buf->grefs)
>> +		return -ENOMEM;
>> +
>> +	buf->directory = kcalloc(num_pages_dir, XEN_PAGE_SIZE, GFP_KERNEL);
>> +	if (!buf->directory)
>> +		goto fail;
>> +
>> +	buf->buffer_sz = num_pages_buffer * XEN_PAGE_SIZE;
>> +	buf->buffer = alloc_pages_exact(buf->buffer_sz, GFP_KERNEL);
>> +	if (!buf->buffer)
>> +		goto fail;
>> +
>> +	return 0;
>> +
>> +fail:
>> +	kfree(buf->grefs);
>> +	buf->grefs = NULL;
>> +	kfree(buf->directory);
> Why do you need to free those here? Shouldn't that be done via
> xen_snd_front_shbuf_free() in case of an error?
At this place we only allocate memory, but xen_snd_front_shbuf_free
will also try to gnttab_end_foreign_access if buf->grefs != NULL.
> Juergen