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<924f4e449a77c50aa03ab0267028fe876b0a6308.camel@linux.ibm.com> Subject: Re: [PATCH v3 2/3] vfio/ism: Implement vfio_pci driver for ISM devices From: Niklas Schnelle To: Julian Ruess , wintera@linux.ibm.com, ts@linux.ibm.com, oberpar@linux.ibm.com, gbayer@linux.ibm.com, Alex Williamson , Jason Gunthorpe , Yishai Hadas , Shameer Kolothum , Kevin Tian Cc: mjrosato@linux.ibm.com, alifm@linux.ibm.com, raspl@linux.ibm.com, hca@linux.ibm.com, agordeev@linux.ibm.com, gor@linux.ibm.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, linux-pci@vger.kernel.org In-Reply-To: <20260305-vfio_pci_ism-v3-2-1217076c81d9@linux.ibm.com> References: <20260305-vfio_pci_ism-v3-0-1217076c81d9@linux.ibm.com> <20260305-vfio_pci_ism-v3-2-1217076c81d9@linux.ibm.com> Autocrypt: addr=schnelle@linux.ibm.com; prefer-encrypt=mutual; keydata=mQINBGHm3M8BEAC+MIQkfoPIAKdjjk84OSQ8erd2OICj98+GdhMQpIjHXn/RJdCZLa58k /ay5x0xIHkWzx1JJOm4Lki7WEzRbYDexQEJP0xUia0U+4Yg7PJL4Dg/W4Ho28dRBROoJjgJSLSHwc 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classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2602130000 definitions=main-2603050103 On Thu, 2026-03-05 at 13:20 +0100, Julian Ruess wrote: > Add a vfio_pci variant driver for the s390-specific Internal Shared > Memory (ISM) devices used for inter-VM communication. >=20 > This enables the development of vfio-pci-based user space drivers for > ISM devices. >=20 > On s390, kernel primitives such as ioread() and iowrite() are switched > over from function handle based PCI load/stores instructions to PCI > memory-I/O (MIO) loads/stores when these are available and not > explicitly disabled. Since these instructions cannot be used with ISM > devices, ensure that classic function handle-based PCI instructions are > used instead. >=20 > The driver is still required even when MIO instructions are disabled, as > the ISM device relies on the PCI store block (PCISTB) instruction to > perform write operations. >=20 > Stores are not fragmented, therefore one ioctl corresponds to exactly > one PCISTB instruction. User space must ensure to not write more than > 4096 bytes at once to an ISM BAR which is the maximum payload of the > PCISTB instruction. >=20 > Reviewed-by: Niklas Schnelle > Signed-off-by: Julian Ruess > --- Just to make it explicit, my R-b stands based on having talked through the changes since v2 with Julian off list. Thanks, Niklas