Re: [Xen-devel] [V5] x86/xsaves: fix overwriting between non-lazy/lazy xsaves

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.03.16 at 07:14, <shuai.ruan@xxxxxxxxxxxxxxx> wrote:
> On Wed, Mar 23, 2016 at 10:02:24AM +0800, Shuai Ruan wrote:
> But for hvm_vcpu_reset_state(), I think we should deleting the code
> initializing the xcomp_bv as said below.
>> For hvm_vcpu_reset_state(), we should depend on whether xsaves is used 
>> to decide whether to init xcomp_bv or not. And currently we use
>> xcr0_accum to indicate the use of xsaves, when hvm_vcpu_reset_state()
>> is called , can vcpu->xcr0_accum indicate using of xsaves ?
>> I think in hvm_vcpu_reset_state(), we should leave xcomp_bv zero.

Leaving it to be zero would be fine, but is it guaranteed to be
zero?

>> > Since again you repeat the same logic twice, this should again have
>> > been a signal that all your changes should go into the XRSTOR()
>> > macro. Or alternatively, since the exception fixup also differs, you
>> > may want to convert the whole logic into an XSAVES and an XSAVE
>> > path. My only really sincere request here is - as little redundancy as
>> > possible, since having to change the same thing twice in more than
>> > one place is always calling for trouble.
> I will do all changes only in XRSTOR(). Code like : 
> 
> #define _XRSTOR(pfx, xrstor_ins)
>        asm volatile ( "1: .byte " pfx xrstor_ins"\n" \
>                             "3:\n" \
>                     "   .section .fixup,\"ax\"\n" \
>                     "2: incl %[faults]\n" \
>                     "   jmp 3b\n" \
>                     "   .previous\n" \
>                       _ASM_EXTABLE(1b, 2b) \
>                       : [mem] "+m" (*ptr), [faults] "+g" (faults) \
>                       : [lmask] "a" (lmask), [hmask] "d" (hmask), \
>                       [ptr] "D" (ptr) )
> 
> #define XRSTOR(pfx) \
>             if ( v->arch.xcr0_accum & XSTATE_XSAVES_ONLY ) \
>             { \
>                 if ( unlikely(!(ptr->xsave_hdr.xcomp_bv \
>                                 & XSTATE_COMPACTION_ENABLED)) ) \
>                     ptr->xsave_hdr.xcomp_bv |= (ptr->xsave_hdr.xstate_bv \
>                                                 | XSTATE_COMPACTION_ENABLED); 
> \
>               _XRSTOR("0x48, ", "0x0f,0xc7,0x1f"); \

I think you mean to use pfx here. Also I don't see the point of
passing two string literals to the auxiliary macro - just pass them
as a single argument.

> A now wapper is intruduced as "_XRSTOR"( maybe the macro name is not
> good ). 

Indeed an underscore followed by an uppercase letter is starting
a reserved identifier. Maybe DO_XRSTOR() or _xrstor()?

Jan


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