Re: [Xen-devel] [PATCH 2/3] x86: also show FS/GS base addresses when dumping registers

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.10.17 at 16:56, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 20/10/17 15:23, Jan Beulich wrote:
>> Their state may be important to figure the reason for a crash. To not
>> further grow duplicate code, break out a helper function.
>>
>> I realize that (ab)using the control register array here may not be
>> considered the nicest solution, but it seems easier (and less overall
>> overhead) to do so compared to the alternative of introducing another
>> helper structure.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> Printing this information is definitely a good idea.
> 
> Reviewed-by Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, with two
> observations.

Thanks.

>> --- a/xen/arch/x86/x86_64/traps.c
>> +++ b/xen/arch/x86/x86_64/traps.c
>> @@ -36,6 +36,21 @@ static void print_xen_info(void)
>>  
>>  enum context { CTXT_hypervisor, CTXT_pv_guest, CTXT_hvm_guest };
>>  
> 
> /* (ab)use crs[5..7] for fs/gs bases. */
> 
> ?  A comment to this effect at least makes it clear that this is
> intentional.

Okay.

>> +static void read_registers(struct cpu_user_regs *regs, unsigned long crs[8])
>> +{
>> +    crs[0] = read_cr0();
>> +    crs[2] = read_cr2();
>> +    crs[3] = read_cr3();
>> +    crs[4] = read_cr4();
>> +    regs->ds = read_sreg(ds);
>> +    regs->es = read_sreg(es);
>> +    regs->fs = read_sreg(fs);
>> +    regs->gs = read_sreg(gs);
>> +    crs[5] = rdfsbase();
>> +    crs[6] = rdgsbase();
>> +    rdmsrl(MSR_SHADOW_GS_BASE, crs[7]);
>> +}
>> +
>>  static void _show_registers(
>>      const struct cpu_user_regs *regs, unsigned long crs[8],
>>      enum context context, const struct vcpu *v)
>> @@ -146,6 +160,7 @@ void show_registers(const struct cpu_use
>>  void vcpu_show_registers(const struct vcpu *v)
>>  {
>>      const struct cpu_user_regs *regs = &v->arch.user_regs;
>> +    bool_t kernel = guest_kernel_mode(v, regs);
> 
> Forward porting mishap?

Oops, indeed.

Jan


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