> -----Original Message----- > From: Eric Auger <[email protected]> > Sent: 27 October 2025 14:26 > To: Nicolin Chen <[email protected]>; Shameer Kolothum > <[email protected]> > Cc: [email protected]; [email protected]; > [email protected]; Jason Gunthorpe <[email protected]>; > [email protected]; [email protected]; Nathan Chen > <[email protected]>; Matt Ochs <[email protected]>; > [email protected]; [email protected]; > [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected] > Subject: Re: [PATCH v4 19/27] hw/arm/smmuv3-accel: Install S1 bypass hwpt > on reset > > External email: Use caution opening links or attachments > > > On 10/17/25 1:19 AM, Nicolin Chen wrote: > > On Mon, Sep 29, 2025 at 02:36:35PM +0100, Shameer Kolothum wrote: > >> When the guest reboots with devices in nested mode (S1 + S2), any > QEMU/UEFI > >> access to those devices can fail because S1 translation is not valid during > >> the reboot. For example, a passthrough NVMe device may hold GRUB boot > info > >> that UEFI tries to read during the reboot. > >> > >> Set S1 to bypass mode during reset to avoid such failures. > > GBPA is set to bypass on reset so I think it's fine. Yet, maybe the > > code should check that. > > shouldn't we check its actual value before setting bypass? > > By the way the spec says is ABORT is set to 0x0: > "Do not abort incoming transactions. Transactions bypass the SMMU with > attributes given by other fields in this register." > > Wondering about those attributes and they can apply on the host?
That’s right. There are other attributes there. Currently kernel only support, * @ste: The first two double words of the user space Stream Table Entry for * the translation. Must be little-endian. * Allowed fields: (Refer to "5.2 Stream Table Entry" in SMMUv3 HW Spec) * - word-0: V, Cfg, S1Fmt, S1ContextPtr, S1CDMax * - word-1: EATS, S1DSS, S1CIR, S1COR, S1CSH, S1STALLD If other attributes make sense, we may have to update kernel. I will add a note here, so that we can update it if required. I think Nicolin is looking into this. Thanks, Shameer
