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Date: Mon, 2 May 2022 15:31:41 +0200
From: Juergen Gross <jgross@...e.com>
To: Oleksandr <olekstysh@...il.com>,
xen-devel <xen-devel@...ts.xenproject.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Stefano Stabellini <sstabellini@...nel.org>
Subject: Re: [PATCH v2 08/19] xen/shbuf: switch xen-front-pgdir-shbuf to use
INVALID_GRANT_REF
On 29.04.22 17:28, Oleksandr wrote:
>
> Hello Juergen
>
>
> On 28.04.22 21:03, Oleksandr Tyshchenko wrote:
>>
>>
>> On Thu, Apr 28, 2022 at 11:28 AM Juergen Gross <jgross@...e.com
>> <mailto:jgross@...e.com>> wrote:
>>
>> Hello Juergen
>>
>> [sorry for the possible format issue]
>>
>> Instead of using a private macro for an invalid grant reference use
>> the common one.
>>
>> Signed-off-by: Juergen Gross <jgross@...e.com
>> <mailto:jgross@...e.com>>
>> ---
>> drivers/xen/xen-front-pgdir-shbuf.c | 17 ++++-------------
>> 1 file changed, 4 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/xen/xen-front-pgdir-shbuf.c
>> b/drivers/xen/xen-front-pgdir-shbuf.c
>> index a959dee21134..fa2921d4fbfc 100644
>> --- a/drivers/xen/xen-front-pgdir-shbuf.c
>> +++ b/drivers/xen/xen-front-pgdir-shbuf.c
>> @@ -21,15 +21,6 @@
>>
>> #include <xen/xen-front-pgdir-shbuf.h>
>>
>> -#ifndef GRANT_INVALID_REF
>> -/*
>> - * FIXME: usage of grant reference 0 as invalid grant reference:
>> - * grant reference 0 is valid, but never exposed to a PV driver,
>> - * because of the fact it is already in use/reserved by the PV
>> console.
>> - */
>> -#define GRANT_INVALID_REF 0
>> -#endif
>> -
>> /**
>> * This structure represents the structure of a shared page
>> * that contains grant references to the pages of the shared
>> @@ -83,7 +74,7 @@ grant_ref_t
>> xen_front_pgdir_shbuf_get_dir_start(struct xen_front_pgdir_shbuf
>> *buf)
>> {
>> if (!buf->grefs)
>> - return GRANT_INVALID_REF;
>> + return INVALID_GRANT_REF;
>>
>> return buf->grefs[0];
>> }
>> @@ -142,7 +133,7 @@ void xen_front_pgdir_shbuf_free(struct
>> xen_front_pgdir_shbuf *buf)
>> int i;
>>
>> for (i = 0; i < buf->num_grefs; i++)
>> - if (buf->grefs[i] != GRANT_INVALID_REF)
>> + if (buf->grefs[i] != INVALID_GRANT_REF)
>> gnttab_end_foreign_access(buf->grefs[i], 0UL);
>> }
>> kfree(buf->grefs);
>> @@ -355,7 +346,7 @@ static void backend_fill_page_dir(struct
>> xen_front_pgdir_shbuf *buf)
>> }
>> /* Last page must say there is no more pages. */
>> page_dir = (struct xen_page_directory *)ptr;
>> - page_dir->gref_dir_next_page = GRANT_INVALID_REF;
>> + page_dir->gref_dir_next_page = INVALID_GRANT_REF;
>> }
>>
>> /**
>> @@ -384,7 +375,7 @@ static void guest_fill_page_dir(struct
>> xen_front_pgdir_shbuf *buf)
>>
>> if (grefs_left <= XEN_NUM_GREFS_PER_PAGE) {
>> to_copy = grefs_left;
>> - page_dir->gref_dir_next_page =
>> GRANT_INVALID_REF;
>> + page_dir->gref_dir_next_page =
>> INVALID_GRANT_REF;
>>
>>
>> I faced an issue with testing PV Sound with the current series.
>>
>> root@...vator-x-h3-4x2g-xt-domu:~# aplay /media/MoodyLoop.wav
>> Playing WAVE '/media/MoodyLoop.wav' : Signed 16 bit Little Endian, Rate 44100
>> Hz, Stereo
>> (XEN) common/grant_table.c:1053:d1v2 Bad ref 0xffffffff for d6
>>
>> Here we have an interesting situation. PV Sound frontend uses this
>> xen-front-pgdir-shbuf framework. Technically, this patch changes
>> page_dir->gref_dir_next_page (reference to the next page describing page
>> directory) from 0 to 0xffffffff here.
>> #define INVALID_GRANT_REF ((grant_ref_t)-1)
>>
>> But according to the protocol (sndif.h), "0" means that there are no more
>> pages in the list and the user space backend expects only that value. So
>> receiving 0xffffffff it assumes there are pages in the list and trying to
>> process...
>> https://elixir.bootlin.com/linux/v5.18-rc4/source/include/xen/interface/io/sndif.h#L650
>>
>>
>>
>> I think, the same is relevant to backend_fill_page_dir() as well.
>
>
> In addition to what I said yesterday:
>
> PV Display also uses this xen-front-pgdir-shbuf framework. It's protocol
> (displif.h) also mentions the same as sndif.h if the context of gref_dir_next_page:
>
> * gref_dir_next_page - grant_ref_t, reference to the next page describing
> * page directory. Must be 0 if there are no more pages in the list.
>
>
> With that local change both PV devices work in my environment.
>
> diff --git a/drivers/xen/xen-front-pgdir-shbuf.c
> b/drivers/xen/xen-front-pgdir-shbuf.c
> index fa2921d..ad4a88e 100644
> --- a/drivers/xen/xen-front-pgdir-shbuf.c
> +++ b/drivers/xen/xen-front-pgdir-shbuf.c
> @@ -346,7 +346,7 @@ static void backend_fill_page_dir(struct
> xen_front_pgdir_shbuf *buf)
> }
> /* Last page must say there is no more pages. */
> page_dir = (struct xen_page_directory *)ptr;
> - page_dir->gref_dir_next_page = INVALID_GRANT_REF;
> + page_dir->gref_dir_next_page = 0;
> }
>
> /**
> @@ -375,7 +375,7 @@ static void guest_fill_page_dir(struct xen_front_pgdir_shbuf
> *buf)
>
> if (grefs_left <= XEN_NUM_GREFS_PER_PAGE) {
> to_copy = grefs_left;
> - page_dir->gref_dir_next_page = INVALID_GRANT_REF;
> + page_dir->gref_dir_next_page = 0;
> } else {
> to_copy = XEN_NUM_GREFS_PER_PAGE;
> page_dir->gref_dir_next_page = buf->grefs[i + 1];
I think I'll introduce a proper define for that purpose.
Juergen
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