On Mon, Jun 30, 2025 at 9:39 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > On Wed, Jun 25 2025 at 21:47, Anup Patel wrote: > > $Subject... > > https://www.kernel.org/doc/html/latest/process/maintainer-tip.html#patch-subject > > Is it that hard? Not sure why I chose a different subject prefix this time. I will update this in the next revision. > > > When injecting IPIs to a set of harts, the IMSIC IPI support will > > do a separate MMIO write to SETIPNUM_LE register of each target > > hart. This means on a platform where IMSIC is trap-n-emulated, > > there will be N MMIO traps when injecting IPI to N target harts > > hence IPIs based on IMSIC software injected MSI is slow compared > > to the SBI IPI extension. > > > > Add a kernel parameter to disable IPIs in IMSIC driver for platforms > > with trap-n-emulated IMSIC. > > Why do you need a kernel parameter for that. If the platform uses trap-n > emulation, then disable the IPI muck automatically, no? > Unfortunately, we don't have DT, ACPI, or any other way of discovering whether underlying IMSIC is trap-n-emulated. In fact, the DT or ACPI passed to a KVM Guest is the same irrespective of whether underlying IMSIC is trap-n-emulated or backed by hardware IMSIC VS-file. Using software injected MSIs as IPIs is purely a software choice in the IMSIC driver so this new kernel parameter allows users to override it. Regards, Anup
