On Wed, Jul 05, 2023 at 09:33:26AM -0300, Daniel Henrique Barboza wrote: > > > On 7/5/23 09:18, Alexandre Ghiti wrote: > > > > On 05/07/2023 11:15, Daniel Henrique Barboza wrote: > > > KVM userspaces need to be aware of the host SATP to allow them to > > > advertise it back to the guest OS. > > > > > > Since this information is used to build the guest FDT we can't wait for > > > > > > The thing is the "mmu-type" property in the FDT is never used: the kernel will probe the hardware and choose the largest available mode, or use "no4lvl"/"no5lvl" from the command line to restrict this mode. And FYI the current mode is exposed through cpuinfo. @Conor Can we deprecate this node or something similar? > > > > Just a remark, not sure that helps :) > > It does, thanks. I am aware that the current mode is exposed through cpuinfo. > mvendorid/marchid/mimpid is also exposed there. As far as I understand we should > rely on KVM to provide all CPU related info to configure a vcpu though. > > A little background of where I'm coming from. One of the QEMU KVM cpu types (host) > doesn't have an assigned satp_mode. The FDT creation of the 'virt' board relies on > that info being present, and the result is that the board will segfault. I sent a > fix for it that I hope will be queued shortly: > > https://lore.kernel.org/qemu-devel/20230630100811.287315-3-dbarboza@xxxxxxxxxxxxxxxx/ > > Thus, if it's decided that the satp_mode FDT is deprecated, we can ignore this > patch altogether. Thanks, We'll eventually want the ability to get and set vsatp.mode from the VMM, so we'll want KVM_REG_RISCV_CONFIG_REG(satp_mode) anyway. For now, since we only support CPU passthrough with KVM, it's a convenient way to read the host's mode (while PPC qemu-kvm does read cpuinfo, I'm not aware of any other qemu-kvm doing that). Thanks, drew
