diff mbox

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

Message ID 20180416062453.24743-5-andr2000@gmail.com (mailing list archive)
State New, archived
Headers show

Commit Message

Oleksandr Andrushchenko April 16, 2018, 6:24 a.m. UTC
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

Comments

Jürgen Groß April 16, 2018, 1:39 p.m. UTC | #1
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?

> +
>  	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?


Juergen
Oleksandr Andrushchenko April 17, 2018, 9:22 a.m. UTC | #2
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
Jürgen Groß April 17, 2018, 11:15 a.m. UTC | #3
On 17/04/18 11:22, Oleksandr Andrushchenko wrote:
> On 04/16/2018 04:39 PM, Juergen Gross wrote:
>> On 16/04/18 08:24, Oleksandr Andrushchenko wrote:
>>> +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.

Okay.


Juergen
diff mbox

Patch

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;
+	}
+
 	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);
+	buf->directory = NULL;
+	return -ENOMEM;
+}
+
+int xen_snd_front_shbuf_alloc(struct xenbus_device *xb_dev,
+			      struct xen_snd_front_shbuf *buf,
+			      unsigned int buffer_sz)
+{
+	int num_pages_buffer, num_pages_dir, num_grefs;
+	int ret;
+
+	xen_snd_front_shbuf_clear(buf);
+
+	num_pages_buffer = DIV_ROUND_UP(buffer_sz, XEN_PAGE_SIZE);
+	/* number of pages the page directory consumes itself */
+	num_pages_dir = DIV_ROUND_UP(num_pages_buffer,
+				     XENSND_NUM_GREFS_PER_PAGE);
+	num_grefs = num_pages_buffer + num_pages_dir;
+
+	ret = alloc_int_buffers(buf, num_pages_dir,
+				num_pages_buffer, num_grefs);
+	if (ret < 0)
+		return ret;
+
+	ret = grant_references(xb_dev, buf, num_pages_dir, num_pages_buffer,
+			       num_grefs);
+	if (ret < 0)
+		return ret;
+
+	fill_page_dir(buf, num_pages_dir);
+	return 0;
+}
diff --git a/sound/xen/xen_snd_front_shbuf.h b/sound/xen/xen_snd_front_shbuf.h
new file mode 100644
index 000000000000..d28e97c47b2c
--- /dev/null
+++ b/sound/xen/xen_snd_front_shbuf.h
@@ -0,0 +1,36 @@ 
+/* 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>
+ */
+
+#ifndef __XEN_SND_FRONT_SHBUF_H
+#define __XEN_SND_FRONT_SHBUF_H
+
+#include <xen/grant_table.h>
+
+#include "xen_snd_front_evtchnl.h"
+
+struct xen_snd_front_shbuf {
+	int num_grefs;
+	grant_ref_t *grefs;
+	u8 *directory;
+	u8 *buffer;
+	size_t buffer_sz;
+};
+
+grant_ref_t xen_snd_front_shbuf_get_dir_start(struct xen_snd_front_shbuf *buf);
+
+int xen_snd_front_shbuf_alloc(struct xenbus_device *xb_dev,
+			      struct xen_snd_front_shbuf *buf,
+			      unsigned int buffer_sz);
+
+void xen_snd_front_shbuf_clear(struct xen_snd_front_shbuf *buf);
+
+void xen_snd_front_shbuf_free(struct xen_snd_front_shbuf *buf);
+
+#endif /* __XEN_SND_FRONT_SHBUF_H */