From 595d153dd1022392083ac93a1550382cbee127e0 Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Tue, 26 May 2020 16:18:08 +1000 Subject: [PATCH] powerpc/64s: Fix restore of NV GPRs after facility unavailable exception Commit 702f09805222 ("powerpc/64s/exception: Remove lite interrupt return") changed the interrupt return path to not restore non-volatile registers by default, and explicitly restore them in paths where it is required. But it missed that the facility unavailable exception can sometimes modify user registers, ie. when it does emulation of move from DSCR. This is seen as a failure of the dscr_sysfs_thread_test: test: dscr_sysfs_thread_test [cpu 0] User DSCR should be 1 but is 0 failure: dscr_sysfs_thread_test So restore non-volatile GPRs after facility unavailable exceptions. Currently the hypervisor facility unavailable exception is also wired up to call facility_unavailable_exception(). In practice we should never take a hypervisor facility unavailable exception for the DSCR. On older bare metal systems we set HFSCR_DSCR unconditionally in __init_HFSCR, or on newer systems it should be enabled via the "data-stream-control-register" device tree CPU feature. Even if it's not, since commit f3c99f97a3cd ("KVM: PPC: Book3S HV: Don't access HFSCR, LPIDR or LPCR when running nested"), the KVM code has unconditionally set HFSCR_DSCR when running guests. So we should only get a hypervisor facility unavailable for the DSCR if skiboot has disabled the "data-stream-control-register" feature, and we are somehow in guest context but not via KVM. Given all that, it should be unnecessary to add a restore of non-volatile GPRs after the hypervisor facility exception, because we never expect to hit that path. But equally we may as well add the restore, because we never expect to hit that path, and if we ever did, at least we would correctly restore the registers to their post emulation state. In future we can split the non-HV and HV facility unavailable handling so that there is no emulation in the HV handler, and then remove the restore for the HV case. Fixes: 702f09805222 ("powerpc/64s/exception: Remove lite interrupt return") Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200526061808.2472279-1-mpe@ellerman.id.au --- arch/powerpc/kernel/exceptions-64s.S | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S index b0ad930cbae5..ebeebab74b56 100644 --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -2411,6 +2411,7 @@ EXC_COMMON_BEGIN(facility_unavailable_common) GEN_COMMON facility_unavailable addi r3,r1,STACK_FRAME_OVERHEAD bl facility_unavailable_exception + REST_NVGPRS(r1) /* instruction emulation may change GPRs */ b interrupt_return GEN_KVM facility_unavailable @@ -2440,6 +2441,7 @@ EXC_COMMON_BEGIN(h_facility_unavailable_common) GEN_COMMON h_facility_unavailable addi r3,r1,STACK_FRAME_OVERHEAD bl facility_unavailable_exception + REST_NVGPRS(r1) /* XXX Shouldn't be necessary in practice */ b interrupt_return GEN_KVM h_facility_unavailable -- 2.20.1