On 64-bit kernels, MIPS KVM will clear CP0_Status.UX to prevent the guest (running in user mode) from accessing the 64-bit memory segments. However the previous value of CP0_Status.UX is never restored when exiting from the guest. If the user process uses 64-bit addressing (the n64 ABI) this can result in address error exceptions from the kernel if it needs to deliver a signal before returning to user mode, as the kernel will need to write a sigframe to high user addresses on the user stack which are disallowed by CP0_Status.UX=0. This is fixed by explicitly setting SX and UX again when exiting from the guest, and explicitly clearing those bits when returning to the guest. Having the SX and UX bits set when handling guest exits (rather than only when exiting to userland) will be helpful when we support VZ, since we shouldn't need to directly read or write guest memory, so it will be valid for cache management IPIs to access host user addresses. Signed-off-by: James Hogan <james.hogan@xxxxxxxxxx> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: "Radim Krčmář" <rkrcmar@xxxxxxxxxx> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx> Cc: linux-mips@xxxxxxxxxxxxxx Cc: kvm@xxxxxxxxxxxxxxx Cc: <stable@xxxxxxxxxxxxxxx> # 4.8.x- --- arch/mips/kvm/entry.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/mips/kvm/entry.c b/arch/mips/kvm/entry.c index 6a02b3a3fa65..e92fb190e2d6 100644 --- a/arch/mips/kvm/entry.c +++ b/arch/mips/kvm/entry.c @@ -521,6 +521,9 @@ void *kvm_mips_build_exit(void *addr) uasm_i_and(&p, V0, V0, AT); uasm_i_lui(&p, AT, ST0_CU0 >> 16); uasm_i_or(&p, V0, V0, AT); +#ifdef CONFIG_64BIT + uasm_i_ori(&p, V0, V0, ST0_SX | ST0_UX); +#endif uasm_i_mtc0(&p, V0, C0_STATUS); uasm_i_ehb(&p); @@ -643,7 +646,7 @@ static void *kvm_mips_build_ret_to_guest(void *addr) /* Setup status register for running guest in UM */ uasm_i_ori(&p, V1, V1, ST0_EXL | KSU_USER | ST0_IE); - UASM_i_LA(&p, AT, ~(ST0_CU0 | ST0_MX)); + UASM_i_LA(&p, AT, ~(ST0_CU0 | ST0_MX | ST0_SX | ST0_UX)); uasm_i_and(&p, V1, V1, AT); uasm_i_mtc0(&p, V1, C0_STATUS); uasm_i_ehb(&p); -- git-series 0.8.10
