On 24.11.17 00:33, Greg Kurz wrote: > On Wed, 22 Nov 2017 14:42:21 +1100 > Alexey Kardashevskiy <aik@xxxxxxxxx> wrote: > >> 96df226 "KVM: PPC: Book3S PR: Preserve storage control bits" added WIMG >> bits preserving but it missed 2 special cases: >> - a magic page in kvmppc_mmu_book3s_64_xlate() and >> - guest real mode in kvmppc_handle_pagefault(). >> >> For these ptes WIMG were 0 and pHyp failed on these causing a guest to >> stop in the very beginning at NIP=0x100 (due to bd9166ffe >> "KVM: PPC: Book3S PR: Exit KVM on failed mapping"). >> >> This initializes WIMG to non-zero value HPTE_R_M. The value is chosen >> as (0x192 & HPTE_R_WIMG); 0x192 is a magic value from >> kvmppc_mmu_map_page(). >> >> Fixes: 96df226 "KVM: PPC: Book3S PR: Preserve storage control bits" >> Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx> >> --- >> >> This indeed fixes PR KVM + VFIO under pHyp but selection of HPTE_R_M >> is arguable. >> > > The initial page fault at 0x100 on machine startup causes H_ENTER to fail in > pHyp with H_PARAMETER, as described in PAPR: > > The hypervisor checks that the WIMG bits within the PTE are appropriate for the > physical page number else H_Parameter return. (For System Memory pages WIMG=0010, > or, 1110 if the SAO option is enabled, and for IO pages WIMG=01**.) > > I'm not aware we care for SAO so HPTE_R_M looks like the only sensible choice, > or I'm missing something ? > > Anyway, this patch allows to start a PR guest on PowerVM again. > > Reviewed-by: Greg Kurz <groug@xxxxxxxx> > > and > > Tested-by: Greg Kurz <groug@xxxxxxxx> So doesn't that mean we should pick it up, mark it CC stable and push it upstream? Alex
