Hi Christoffer, On Thu, 2015-02-19 at 21:57 +0100, Christoffer Dall wrote: > On Fri, Jan 30, 2015 at 03:33:48PM -0800, Geoff Levand wrote: > > To allow for additional hcalls to be defined and to make the arm64 hcall API > > more consistent across exception vector routines, change the hcall implementations > > to use the ISS field of the ESR_EL2 register to specify the hcall type. > > how does this make things more consistent? Do we have other examples of > things using the immediate field which I'm missing? As I detail in the next paragraph, by consistent I mean in the API exposed, not in the implementation. This point is really secondary to the need for more hyper calls as I discuss below. > > The existing arm64 hcall implementations are limited in that they only allow > > for two distinct hcalls; with the x0 register either zero, or not zero. Also, > > the API of the hyp-stub exception vector routines and the KVM exception vector > > routines differ; hyp-stub uses a non-zero value in x0 to implement > > __hyp_set_vectors, whereas KVM uses it to implement kvm_call_hyp. > > this seems orthogonal to the use of the immediate field vs. x0 though, > so why it the immediate field preferred again? When a CPU is reset via cpu_soft_restart() we need to execute the caller supplied reset routine at the exception level the kernel was entered at. So, for a kernel entered at EL2, we need a way to execute that routine at EL2. The current hyp-stub vector implementation, which uses x0, is limited to two hyper calls; __hyp_get_vectors and __hyp_set_vectors. To support cpu_soft_restart() we need a third hyper call, one which allows for code to be executed at EL2. My proposed use of the immediate value of the hvc instruction will allow for 2^16 distinct hyper calls. > > Define three new preprocessor macros HVC_CALL_HYP, HVC_GET_VECTORS, and > > HVC_SET_VECTORS to be used as hcall type specifiers and convert the > > existing __hyp_get_vectors(), __hyp_set_vectors() and kvm_call_hyp() routines > > to use these new macros when executing an HVC call. Also change the > > corresponding hyp-stub and KVM el1_sync exception vector routines to use these > > new macros. > > > > Signed-off-by: Geoff Levand <geoff at infradead.org> > > --- > > arch/arm64/include/asm/virt.h | 27 +++++++++++++++++++++++++++ > > arch/arm64/kernel/hyp-stub.S | 32 +++++++++++++++++++++----------- > > arch/arm64/kernel/psci.c | 3 ++- > > arch/arm64/kvm/hyp.S | 16 +++++++++------- > > 4 files changed, 59 insertions(+), 19 deletions(-) > > > > diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h > > index 7a5df52..eb10368 100644 > > --- a/arch/arm64/include/asm/virt.h > > +++ b/arch/arm64/include/asm/virt.h > > @@ -18,6 +18,33 @@ > > #ifndef __ASM__VIRT_H > > #define __ASM__VIRT_H > > > > +/* > > + * The arm64 hcall implementation uses the ISS field of the ESR_EL2 register to > > + * specify the hcall type. The exception handlers are allowed to use registers > > + * x17 and x18 in their implementation. Any routine issuing an hcall must not > > + * expect these registers to be preserved. > > + */ > > I thought the existing use of registers were based on the arm procedure > call standard so we didn't have to worry about adding more caller-save > registers. > > Don't we now have to start adding code around callers to make sure > callers know that x17 and x18 may be clobbered? We use x17 and x18 to allow hyper calls to work without a stack, which is needed for cpu_soft_restart(). The procedure call standard says that these are temporary registers, so a C compiler should not expect these to be preserved. -Geoff
