On 10/08/2013 01:22 PM, Paul Mackerras wrote:
> On Mon, Oct 07, 2013 at 04:27:47PM +0200, 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.
>>
>> Finally, kvmppc_emulate_instruction() uses kvmppc_is_bigendian()
>> to define in which endian order the mmio needs to be done.
>>
>> Signed-off-by: Cédric Le Goater <[email protected]>
>
> [snip]
>
>> + ld r0, VCPU_MSR(r9)
>> +
>> + /* r10 = vcpu->arch.msr & MSR_LE */
>> + rldicl. r10, r0, 0, 63
>
> I would have written:
>
> andi. r10, r0, MSR_LE
>
> which doesn't need the comment, but really the two are equivalent.
Indeed, this is even better ... rldicl is a vestige of an earlier version
of this patch.
>> @@ -232,6 +231,7 @@ 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 is_bigendian = kvmppc_is_bigendian(vcpu);
>>
>> /* this default type might be overwritten by subcategories */
>> kvmppc_set_exit_type(vcpu, EMULATED_INST_EXITS);
>> @@ -266,47 +266,53 @@ int kvmppc_emulate_instruction(struct kvm_run *run,
>> struct kvm_vcpu *vcpu)
>> advance = 0;
>> break;
>> case OP_31_XOP_LWZX:
>> - emulated = kvmppc_handle_load(run, vcpu, rt, 4, 1);
>> + emulated = kvmppc_handle_load(run, vcpu, rt, 4,
>> + is_bigendian);
>
> I see you're still hitting all the call sites of kvmppc_handle_load(),
> kvmppc_handle_loads() and kvmppc_handle_store(), rather than putting
> the big-endian test inside kvmppc_handle_load() and
> kvmppc_handle_store(), as in this untested patch:
>
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index f55e14c..171bce6 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -625,9 +625,13 @@ static void kvmppc_complete_mmio_load(struct kvm_vcpu
> *vcpu,
> }
>
> int kvmppc_handle_load(struct kvm_run *run, struct kvm_vcpu *vcpu,
> - unsigned int rt, unsigned int bytes, int is_bigendian)
> + unsigned int rt, unsigned int bytes, int not_reverse)
> {
> int idx, ret;
> + int is_bigendian = not_reverse;
> +
> + if (!kvmppc_is_bigendian(vcpu))
> + is_bigendian = !not_reverse;
>
> if (bytes > sizeof(run->mmio.data)) {
> printk(KERN_ERR "%s: bad MMIO length: %d\n", __func__,
> @@ -662,21 +666,25 @@ int kvmppc_handle_load(struct kvm_run *run, struct
> kvm_vcpu *vcpu,
>
> /* Same as above, but sign extends */
> int kvmppc_handle_loads(struct kvm_run *run, struct kvm_vcpu *vcpu,
> - unsigned int rt, unsigned int bytes, int
> is_bigendian)
> + unsigned int rt, unsigned int bytes, int not_reverse)
> {
> int r;
>
> vcpu->arch.mmio_sign_extend = 1;
> - r = kvmppc_handle_load(run, vcpu, rt, bytes, is_bigendian);
> + r = kvmppc_handle_load(run, vcpu, rt, bytes, not_reverse);
>
> return r;
> }
>
> int kvmppc_handle_store(struct kvm_run *run, struct kvm_vcpu *vcpu,
> - u64 val, unsigned int bytes, int is_bigendian)
> + u64 val, unsigned int bytes, int not_reverse)
> {
> void *data = run->mmio.data;
> int idx, ret;
> + int is_bigendian = not_reverse;
> +
> + if (!kvmppc_is_bigendian(vcpu))
> + is_bigendian = !not_reverse;
>
> if (bytes > sizeof(run->mmio.data)) {
> printk(KERN_ERR "%s: bad MMIO length: %d\n", __func__,
>
> That seems simpler to me -- is there a reason not to do it that way?
No. A part from the fact I did not quite get what you meant the first
time we talked about it. This is more elegant. I will resend a -v2.
Thanks for the review Paul,
C.
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