On 03.10.2013, at 13:03, Cédric Le Goater wrote:
> MMIO emulation reads the last instruction executed by the guest
> and then emulates. If the guest is running in Little Endian mode,
> the instruction needs to be byte-swapped before being emulated.
>
> This patch stores the last instruction in the endian order of the
> host, primarily doing a byte-swap if needed. The common code
> which fetches last_inst uses a helper routine kvmppc_need_byteswap().
> and the exit paths for the Book3S PV and HR guests use their own
> version in assembly.
>
> kvmppc_emulate_instruction() also uses kvmppc_need_byteswap() to
> define in which endian order the mmio needs to be done.
>
> The patch is based on Alex Graf's kvm-ppc-queue branch and it
> has been tested on Big Endian and Little Endian HV guests and
> Big Endian PR guests.
>
> Signed-off-by: Cédric Le Goater <[email protected]>
> ---
>
> Here are some comments/questions :
>
> * the host is assumed to be running in Big Endian. when Little Endian
> hosts are supported in the future, we will use the cpu features to
> fix kvmppc_need_byteswap()
>
> * the 'is_bigendian' parameter of the routines kvmppc_handle_load()
> and kvmppc_handle_store() seems redundant but the *BRX opcodes
> make the improvements unclear. We could eventually rename the
> parameter to byteswap and the attribute vcpu->arch.mmio_is_bigendian
> to vcpu->arch.mmio_need_byteswap. Anyhow, the current naming sucks
> and I would happy to have some directions to fix it.
>
>
>
> arch/powerpc/include/asm/kvm_book3s.h | 15 ++++++-
> arch/powerpc/kvm/book3s_64_mmu_hv.c | 4 ++
> arch/powerpc/kvm/book3s_hv_rmhandlers.S | 14 +++++-
> arch/powerpc/kvm/book3s_segment.S | 14 +++++-
> arch/powerpc/kvm/emulate.c | 71 +++++++++++++++++--------------
> 5 files changed, 83 insertions(+), 35 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/kvm_book3s.h
> b/arch/powerpc/include/asm/kvm_book3s.h
> index 0ec00f4..36c5573 100644
> --- a/arch/powerpc/include/asm/kvm_book3s.h
> +++ b/arch/powerpc/include/asm/kvm_book3s.h
> @@ -270,14 +270,22 @@ static inline ulong kvmppc_get_pc(struct kvm_vcpu *vcpu)
> return vcpu->arch.pc;
> }
>
> +static inline bool kvmppc_need_byteswap(struct kvm_vcpu *vcpu)
> +{
> + return vcpu->arch.shared->msr & MSR_LE;
> +}
> +
> static inline u32 kvmppc_get_last_inst(struct kvm_vcpu *vcpu)
> {
> ulong pc = kvmppc_get_pc(vcpu);
>
> /* Load the instruction manually if it failed to do so in the
> * exit path */
> - if (vcpu->arch.last_inst == KVM_INST_FETCH_FAILED)
> + if (vcpu->arch.last_inst == KVM_INST_FETCH_FAILED) {
> kvmppc_ld(vcpu, &pc, sizeof(u32), &vcpu->arch.last_inst, false);
> + if (kvmppc_need_byteswap(vcpu))
> + vcpu->arch.last_inst = swab32(vcpu->arch.last_inst);
Could you please introduce a new helper to load 32bit numbers? Something like
kvmppc_ldl or kvmppc_ld32. That'll be easier to read here then :).
> + }
>
> return vcpu->arch.last_inst;
> }
> @@ -293,8 +301,11 @@ static inline u32 kvmppc_get_last_sc(struct kvm_vcpu
> *vcpu)
>
> /* Load the instruction manually if it failed to do so in the
> * exit path */
> - if (vcpu->arch.last_inst == KVM_INST_FETCH_FAILED)
> + if (vcpu->arch.last_inst == KVM_INST_FETCH_FAILED) {
> kvmppc_ld(vcpu, &pc, sizeof(u32), &vcpu->arch.last_inst, false);
> + if (kvmppc_need_byteswap(vcpu))
> + vcpu->arch.last_inst = swab32(vcpu->arch.last_inst);
> + }
>
> return vcpu->arch.last_inst;
> }
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> index 3a89b85..28130c7 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -547,6 +547,10 @@ static int kvmppc_hv_emulate_mmio(struct kvm_run *run,
> struct kvm_vcpu *vcpu,
> ret = kvmppc_ld(vcpu, &srr0, sizeof(u32), &last_inst, false);
> if (ret != EMULATE_DONE || last_inst == KVM_INST_FETCH_FAILED)
> return RESUME_GUEST;
> +
> + if (kvmppc_need_byteswap(vcpu))
> + last_inst = swab32(last_inst);
> +
> vcpu->arch.last_inst = last_inst;
> }
>
> diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> index dd80953..1d3ee40 100644
> --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> @@ -1393,14 +1393,26 @@ fast_interrupt_c_return:
> lwz r8, 0(r10)
> mtmsrd r3
>
> + ld r0, VCPU_MSR(r9)
> +
> + /* r10 = vcpu->arch.msr & MSR_LE */
> + rldicl r10, r0, 0, 63
rldicl.?
> + cmpdi r10, 0
> + bne 2f
I think it makes sense to inline that branch in here instead. Just make this
stw r8, VCPU_LAST_INST(r9)
beq after_inst_store
/* Little endian instruction, swap for big endian hosts */
addi ...
stwbrx ...
after_inst_store:
The duplicate store shouldn't really hurt too badly, but in our "fast path"
we're only doing one store anyway :). And the code becomes more readable.
> +
> /* Store the result */
> stw r8, VCPU_LAST_INST(r9)
>
> /* Unset guest mode. */
> - li r0, KVM_GUEST_MODE_NONE
> +1: li r0, KVM_GUEST_MODE_NONE
> stb r0, HSTATE_IN_GUEST(r13)
> b guest_exit_cont
>
> + /* Swap and store the result */
> +2: addi r11, r9, VCPU_LAST_INST
> + stwbrx r8, 0, r11
> + b 1b
> +
> /*
> * Similarly for an HISI, reflect it to the guest as an ISI unless
> * it is an HPTE not found fault for a page that we have paged out.
> diff --git a/arch/powerpc/kvm/book3s_segment.S
> b/arch/powerpc/kvm/book3s_segment.S
> index 1abe478..bf20b45 100644
> --- a/arch/powerpc/kvm/book3s_segment.S
> +++ b/arch/powerpc/kvm/book3s_segment.S
> @@ -287,7 +287,19 @@ ld_last_inst:
> sync
>
> #endif
> - stw r0, SVCPU_LAST_INST(r13)
> + ld r8, SVCPU_SHADOW_SRR1(r13)
> +
> + /* r10 = vcpu->arch.msr & MSR_LE */
> + rldicl r10, r0, 0, 63
> + cmpdi r10, 0
> + beq 1f
> +
> + /* swap and store the result */
> + addi r11, r13, SVCPU_LAST_INST
> + stwbrx r0, 0, r11
> + b no_ld_last_inst
> +
> +1: stw r0, SVCPU_LAST_INST(r13)
>
> no_ld_last_inst:
>
> diff --git a/arch/powerpc/kvm/emulate.c b/arch/powerpc/kvm/emulate.c
> index 751cd45..20529ca 100644
> --- a/arch/powerpc/kvm/emulate.c
> +++ b/arch/powerpc/kvm/emulate.c
> @@ -232,6 +232,7 @@ int kvmppc_emulate_instruction(struct kvm_run *run,
> struct kvm_vcpu *vcpu)
> int sprn = get_sprn(inst);
> enum emulation_result emulated = EMULATE_DONE;
> int advance = 1;
> + int dont_byteswap = !kvmppc_need_byteswap(vcpu);
The parameter to kvmppc_handle_load is "is_bigendian" which is also the flag
that we interpret for our byte swaps later. I think we should preserve that
semantic. Please call your variable "is_bigendian" and create a separate helper
for that one.
When little endian host kernels come, we only need to change the way
kvmppc_complete_mmio_load and kvmppc_handle_store swap things - probably
according to user space endianness even.
Alex
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