6.6-stable review patch. If anyone has any objections, please let me know.
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From: Nicholas Piggin npiggin@gmail.com
commit dc158d23b33df9033bcc8e7117e8591dd2f9d125 upstream.
Before running a guest, the host process (e.g., QEMU) FP/VEC registers are saved if they were being used, similarly to when the kernel uses FP registers. The guest values are then loaded into regs, and the host process registers will be restored lazily when it uses FP/VEC.
KVM HV has a bug here: the host process registers do get saved, but the user MSR bits remain enabled, which indicates the registers are valid for the process. After they are clobbered by running the guest, this valid indication causes the host process to take on the FP/VEC register values of the guest.
Fixes: 34e119c96b2b ("KVM: PPC: Book3S HV P9: Reduce mtmsrd instructions required to save host SPRs") Cc: stable@vger.kernel.org # v5.17+ Signed-off-by: Nicholas Piggin npiggin@gmail.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://msgid.link/20231122025811.2973-1-npiggin@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/kernel/process.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
--- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -1198,11 +1198,11 @@ void kvmppc_save_user_regs(void)
usermsr = current->thread.regs->msr;
+ /* Caller has enabled FP/VEC/VSX/TM in MSR */ if (usermsr & MSR_FP) - save_fpu(current); - + __giveup_fpu(current); if (usermsr & MSR_VEC) - save_altivec(current); + __giveup_altivec(current);
#ifdef CONFIG_PPC_TRANSACTIONAL_MEM if (usermsr & MSR_TM) {