[PATCH v4 14/14] ARM64: KVM: fix big endian issue in access_vm_reg for 32bit guest

[Victor Kamensky]

Hi Christoffer,

Please see inline.

On 14 June 2014 08:05, Christoffer Dall <christoffer.dall at linaro.org> wrote:
> On Thu, Jun 12, 2014 at 09:30:13AM -0700, Victor Kamensky wrote:
>> Fix issue with 32bit guests running on top of BE KVM host.
>> Indexes of high and low words of 64bit cp15 register are
>> swapped in case of big endian code, since 64bit cp15 state is
>> restored or saved with double word write or read instruction.
>>
>> Define helper macros to access high low words of 64bit cp15
>> register.
>>
>> Signed-off-by: Victor Kamensky <victor.kamensky at linaro.org>
>> ---
>>  arch/arm64/include/asm/kvm_host.h | 8 ++++++++
>>  arch/arm64/kvm/sys_regs.c         | 4 ++--
>>  2 files changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>> index 0a1d697..e9d2e11 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -140,6 +140,14 @@ struct kvm_vcpu_arch {
>>  #define vcpu_sys_reg(v,r)    ((v)->arch.ctxt.sys_regs[(r)])
>>  #define vcpu_cp15(v,r)               ((v)->arch.ctxt.cp15[(r)])
>>
>> +#ifdef CONFIG_CPU_BIG_ENDIAN
>> +#define vcpu_cp15_64_high(v,r) ((v)->arch.ctxt.cp15[((r) + 0)])
>> +#define vcpu_cp15_64_low(v,r) ((v)->arch.ctxt.cp15[((r) + 1)])
>> +#else
>> +#define vcpu_cp15_64_high(v,r) ((v)->arch.ctxt.cp15[((r) + 1)])
>> +#define vcpu_cp15_64_low(v,r) ((v)->arch.ctxt.cp15[((r) + 0)])
>> +#endif
>> +
>>  struct kvm_vm_stat {
>>       u32 remote_tlb_flush;
>>  };
>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> index 8e65e31..71aa9b0 100644
>> --- a/arch/arm64/kvm/sys_regs.c
>> +++ b/arch/arm64/kvm/sys_regs.c
>> @@ -137,9 +137,9 @@ static bool access_vm_reg(struct kvm_vcpu *vcpu,
>>       if (!p->is_aarch32) {
>>               vcpu_sys_reg(vcpu, r->reg) = val;
>>       } else {
>> -             vcpu_cp15(vcpu, r->reg) = val & 0xffffffffUL;
>> +             vcpu_cp15_64_low(vcpu, r->reg) = val & 0xffffffffUL;
>>               if (!p->is_32bit)
>> -                     vcpu_cp15(vcpu, r->reg + 1) = val >> 32;
>> +                     vcpu_cp15_64_high(vcpu, r->reg) = val >> 32;
>>       }
>>       return true;
>>  }
>> --
>> 1.8.1.4
>>
>
> I thought there was a consensus here about handling 64-bit accesses
> through the 64-bit values with the vcpu_sys_reg() interface?  Did you
> give up on this for a particular reason?

I think I missed that. Do you want this patch to look like below?
Personally, I find it a little bit less clear, but I am fine with it
if you like it more. Or you meant something different?

commit 2de73290a809ef8dbaed087ef2f86d662a006e36
Author: Victor Kamensky <victor.kamensky at linaro.org>
Date:   Mon May 12 13:57:21 2014 -0700

    ARM64: KVM: fix big endian issue in access_vm_reg for 32bit guest

    Fix issue with 32bit guests running on top of BE KVM host.
    Indexes of high and low words of 64bit cp15 register are
    swapped in case of big endian code, since 64bit cp15 state is
    restored or saved with double word write or read instruction.

    Define helper macro to access low words of 64bit cp15 register.

    Signed-off-by: Victor Kamensky <victor.kamensky at linaro.org>

diff --git a/arch/arm64/include/asm/kvm_host.h
b/arch/arm64/include/asm/kvm_host.h
index a10803c..fce74ce 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -140,6 +140,12 @@ struct kvm_vcpu_arch {
 #define vcpu_sys_reg(v,r)      ((v)->arch.ctxt.sys_regs[(r)])
 #define vcpu_cp15(v,r)         ((v)->arch.ctxt.cp15[(r)])

+#ifdef CONFIG_CPU_BIG_ENDIAN
+#define vcpu_cp15_64_low(v,r) ((v)->arch.ctxt.cp15[((r) + 1)])
+#else
+#define vcpu_cp15_64_low(v,r) ((v)->arch.ctxt.cp15[((r) + 0)])
+#endif
+
 struct kvm_vm_stat {
        u32 remote_tlb_flush;
 };
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 8e65e31..a5aa1d1 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -134,12 +134,10 @@ static bool access_vm_reg(struct kvm_vcpu *vcpu,
        BUG_ON(!p->is_write);

        val = *vcpu_reg(vcpu, p->Rt);
-       if (!p->is_aarch32) {
+       if (!p->is_aarch32 || !p->is_32bit) {
                vcpu_sys_reg(vcpu, r->reg) = val;
        } else {
-               vcpu_cp15(vcpu, r->reg) = val & 0xffffffffUL;
-               if (!p->is_32bit)
-                       vcpu_cp15(vcpu, r->reg + 1) = val >> 32;
+               vcpu_cp15_64_low(vcpu, r->reg) = val & 0xffffffffUL;
        }
        return true;
 }

Thanks,
Victor

> -Christoffer