Received-SPF: pass (google.com: domain of linux-kernel+bounces-68757-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:40f1:3f00::1 as permitted sender) client-ip=2604:1380:40f1:3f00::1;
From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>
Date: Fri, 16 Feb 2024 16:46:07 +0200 (EET)
To: mhklinux@outlook.com
cc: haiyangz@microsoft.com, wei.liu@kernel.org, decui@microsoft.com, 
    lpieralisi@kernel.org, kw@linux.com, robh@kernel.org, bhelgaas@google.com, 
    linux-pci@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>, 
    linux-hyperv@vger.kernel.org
Subject: Re: [PATCH v2 1/1] PCI: hv: Fix ring buffer size calculation
In-Reply-To: <20240215074823.51014-1-mhklinux@outlook.com>
Message-ID: <0802ce88-c86d-3a74-501f-28393d6112f3@linux.intel.com>
References: <20240215074823.51014-1-mhklinux@outlook.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="8323328-277225830-1708094767=:1097"

  This message is in MIME format.  The first part should be readable text,
  while the remaining parts are likely unreadable without MIME-aware tools.

--8323328-277225830-1708094767=:1097
Content-Type: text/plain; charset=ISO-8859-15
Content-Transfer-Encoding: QUOTED-PRINTABLE

On Wed, 14 Feb 2024, mhkelley58@gmail.com wrote:

> From: Michael Kelley <mhklinux@outlook.com>
>=20
> For a physical PCI device that is passed through to a Hyper-V guest VM,
> current code specifies the VMBus ring buffer size as 4 pages.  But this
> is an inappropriate dependency, since the amount of ring buffer space
> needed is unrelated to PAGE_SIZE. For example, on x86 the ring buffer
> size ends up as 16 Kbytes, while on ARM64 with 64 Kbyte pages, the ring
> size bloats to 256 Kbytes. The ring buffer for PCI pass-thru devices
> is used for only a few messages during device setup and removal, so any
> space above a few Kbytes is wasted.
>=20
> Fix this by declaring the ring buffer size to be a fixed 16 Kbytes.
> Furthermore, use the VMBUS_RING_SIZE() macro so that the ring buffer
> header is properly accounted for, and so the size is rounded up to a
> page boundary, using the page size for which the kernel is built. While
> w/64 Kbyte pages this results in a 64 Kbyte ring buffer header plus a
> 64 Kbyte ring buffer, that's the smallest possible with that page size.
> It's still 128 Kbytes better than the current code.
>=20
> Cc: <stable@vger.kernel.org> # 5.15.x
> Signed-off-by: Michael Kelley <mhklinux@outlook.com>
> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux=
=2Eintel.com>
> ---
> Changes in v2:
> * Use SZ_16K instead of 16 * 1024
> ---
>  drivers/pci/controller/pci-hyperv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>=20
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller=
/pci-hyperv.c
> index 1eaffff40b8d..baadc1e5090e 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -465,7 +465,7 @@ struct pci_eject_response {
>  =09u32 status;
>  } __packed;
> =20
> -static int pci_ring_size =3D (4 * PAGE_SIZE);
> +static int pci_ring_size =3D VMBUS_RING_SIZE(SZ_16K);
> =20
>  /*
>   * Driver specific state.
>=20

Hi,

You forgot to add #include <linux/sizes.h> for it.

With that fixed:

Reviewed-by: Ilpo J=E4rvinen <ilpo.jarvinen@linux.intel.com>

--=20
 i.

--8323328-277225830-1708094767=:1097--