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Date: Fri, 29 Apr 2022 18:28:34 +0300
From: Oleksandr <olekstysh@...il.com>
To: Juergen Gross <jgross@...e.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
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];
(END)
>
> } else {
> to_copy = XEN_NUM_GREFS_PER_PAGE;
> page_dir->gref_dir_next_page =
> buf->grefs[i + 1];
> --
> 2.34.1
>
>
>
>
> --
> Regards,
>
> Oleksandr Tyshchenko
--
Regards,
Oleksandr Tyshchenko
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