Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx> writes:
> Michael Ellerman [mpe@xxxxxxxxxxxxxx] wrote:
>> Claudio Carvalho <cclaudio@xxxxxxxxxxxxx> writes:
>> > From: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
>> >
>> > To enter a secure guest, we have to go through the ultravisor, therefore
>> > we do a ucall when we are entering a secure guest.
>> >
>> > This change is needed for any sort of entry to the secure guest from the
>> > hypervisor, whether it is a return from an hcall, a return from a
>> > hypervisor interrupt, or the first time that a secure guest vCPU is run.
>> >
>> > If we are returning from an hcall, the results are already in the
>> > appropriate registers R3:12, except for R3, R6 and R7. R3 has the status
>> > of the reflected hcall, therefore we move it to R0 for the ultravisor and
>> > set R3 to the UV_RETURN ucall number. R6,7 were used as temporary
>> > registers, hence we restore them.
>>
>> This is another case where some documentation would help people to
>> review the code.
>>
>> > Have fast_guest_return check the kvm_arch.secure_guest field so that a
>> > new CPU enters UV when started (in response to a RTAS start-cpu call).
>> >
>> > Thanks to input from Paul Mackerras, Ram Pai and Mike Anderson.
>> >
>> > Signed-off-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
>> > [ Pass SRR1 in r11 for UV_RETURN, fix kvmppc_msr_interrupt to preserve
>> > the MSR_S bit ]
>> > Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx>
>> > [ Fix UV_RETURN ucall number and arch.secure_guest check ]
>> > Signed-off-by: Ram Pai <linuxram@xxxxxxxxxx>
>> > [ Save the actual R3 in R0 for the ultravisor and use R3 for the
>> > UV_RETURN ucall number. Update commit message and ret_to_ultra comment ]
>> > Signed-off-by: Claudio Carvalho <cclaudio@xxxxxxxxxxxxx>
>> > ---
>> > arch/powerpc/include/asm/kvm_host.h | 1 +
>> > arch/powerpc/include/asm/ultravisor-api.h | 1 +
>> > arch/powerpc/kernel/asm-offsets.c | 1 +
>> > arch/powerpc/kvm/book3s_hv_rmhandlers.S | 40 +++++++++++++++++++----
>> > 4 files changed, 37 insertions(+), 6 deletions(-)
>> >
>> > diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
>> > index cffb365d9d02..89813ca987c2 100644
>> > --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
>> > +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
>> > @@ -36,6 +36,7 @@
>> > #include <asm/asm-compat.h>
>> > #include <asm/feature-fixups.h>
>> > #include <asm/cpuidle.h>
>> > +#include <asm/ultravisor-api.h>
>> >
>> > /* Sign-extend HDEC if not on POWER9 */
>> > #define EXTEND_HDEC(reg) \
>> > @@ -1092,16 +1093,12 @@ BEGIN_FTR_SECTION
>> > END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
>> >
>> > ld r5, VCPU_LR(r4)
>> > - ld r6, VCPU_CR(r4)
>> > mtlr r5
>> > - mtcr r6
>> >
>> > ld r1, VCPU_GPR(R1)(r4)
>> > ld r2, VCPU_GPR(R2)(r4)
>> > ld r3, VCPU_GPR(R3)(r4)
>> > ld r5, VCPU_GPR(R5)(r4)
>> > - ld r6, VCPU_GPR(R6)(r4)
>> > - ld r7, VCPU_GPR(R7)(r4)
>> > ld r8, VCPU_GPR(R8)(r4)
>> > ld r9, VCPU_GPR(R9)(r4)
>> > ld r10, VCPU_GPR(R10)(r4)
>> > @@ -1119,10 +1116,38 @@ BEGIN_FTR_SECTION
>> > mtspr SPRN_HDSISR, r0
>> > END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
>> >
>> > + ld r6, VCPU_KVM(r4)
>> > + lbz r7, KVM_SECURE_GUEST(r6)
>> > + cmpdi r7, 0
>>
>> You could hoist the load of r6 and r7 to here?
>
> we could move 'ld r7' here. r6 is used to restore CR below so
> it (r6) has to stay there?
It's used to restore CR in both paths, so both paths load VCPU_CR(r4)
into r6. So we could instead do that load once, before the branch?
>> > + bne ret_to_ultra
>> > +
>> > + lwz r6, VCPU_CR(r4)
>> > + mtcr r6
>> > +
>> > + ld r7, VCPU_GPR(R7)(r4)
>> > + ld r6, VCPU_GPR(R6)(r4)
>> > ld r0, VCPU_GPR(R0)(r4)
>> > ld r4, VCPU_GPR(R4)(r4)
>> > HRFI_TO_GUEST
>> > b .
>> > +/*
>> > + * We are entering a secure guest, so we have to invoke the ultravisor to do
>> > + * that. If we are returning from a hcall, the results are already in the
>> > + * appropriate registers R3:12, except for R3, R6 and R7. R3 has the status of
>> > + * the reflected hcall, therefore we move it to R0 for the ultravisor and set
>> > + * R3 to the UV_RETURN ucall number. R6,7 were used as temporary registers
>> > + * above, hence we restore them.
>> > + */
>> > +ret_to_ultra:
>> > + lwz r6, VCPU_CR(r4)
>> > + mtcr r6
>> > + mfspr r11, SPRN_SRR1
>> > + mr r0, r3
>> > + LOAD_REG_IMMEDIATE(r3, UV_RETURN)
>>
>> Worth open coding to save three instructions?
>
> Yes, good point:
>
> - LOAD_REG_IMMEDIATE(r3, UV_RETURN)
> +
> + li r3, 0
> + oris r3, r3, (UV_RETURN)@__AS_ATHIGH
> + ori r3, r3, (UV_RETURN)@l
This should do it no?
li r3, 0
oris r3, r3, UV_RETURN
cheers
