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Thu, 06 Aug 2026 06:05:00 -0700 (PDT) From: Ritesh Harjani (IBM) To: Timothy Pearson , linuxppc-dev Cc: Shivaprasad G Bhat , Gaurav Batra Subject: Re: [BUG] VFIO on POWER9 / QEMU fails to allocate 32-bit DMA In-Reply-To: <334689093.41938.1785796754275.JavaMail.zimbra@raptorengineeringinc.com> Date: Thu, 06 Aug 2026 10:57:22 +0530 Message-ID: References: <334689093.41938.1785796754275.JavaMail.zimbra@raptorengineeringinc.com> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list Hi Timothy, Timothy Pearson writes: > On Linux 6.18, and potentially earlier Linux versions, attempting to pass through any PCI device via VFIO that requires 32-bit DMA results in the following error in the guest VM: Can you confirm if you see the same issue on upstream kernel also or is it only till v6.18 kernel? > > [ 11.705413] cx23885 0000:00:02.0: Warning: IOMMU offset too big for device mask > [ 11.709245] cx23885 0000:00:02.0: mask: 0xffffffff, table offset: 0x800000000000000 > > The same devices work correctly on the host kernel. It appears that somehow 32-bit DMA is not available within a pSeries guest on a PowerNV host. By any chance did you do kexec in the guest kernel? Is this issue only hitting with kexec or even with normal boot up of guest kernel is also showing up the same issue? Could you please share the dmesg logs for both guest and host kernel? That might give some more data about this issue. -ritesh