Re: [PATCH 1/5] KVM: PPC: Book3S HV: Fix computation of tlbie operand

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> writes:

> Paul Mackerras <paulus@samba.org> writes:
>
>> The B (segment size) field in the RB operand for the tlbie
>> instruction is two bits, which we get from the top two bits of
>> the first doubleword of the HPT entry to be invalidated.  These
>> bits go in bits 8 and 9 of the RB operand (bits 54 and 55 in IBM
>> bit numbering).
>>
>> The compute_tlbie_rb() function gets these bits as v >> (62 - 8),
>> which is not correct as it will bring in the top 10 bits, not
>> just the top two.  These extra bits could corrupt the AP, AVAL
>> and L fields in the RB value.  To fix this we shift right 62 bits
>> and then shift left 8 bits, so we only get the two bits of the
>> B field.
>
> Good catch.
>
>>
>> The first doubleword of the HPT entry is under the control of the
>> guest kernel.  In fact, Linux guests will always put zeroes in bits
>> 54 -- 61 (IBM bits 2 -- 9), but we should not rely on guests doing
>> this.
>>
>> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
>> Signed-off-by: Paul Mackerras <paulus@samba.org>
>
>
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
>
>> ---
>>  arch/powerpc/include/asm/kvm_book3s_64.h | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/include/asm/kvm_book3s_64.h b/arch/powerpc/include/asm/kvm_book3s_64.h
>> index 0aa8179..a37f1a4 100644
>> --- a/arch/powerpc/include/asm/kvm_book3s_64.h
>> +++ b/arch/powerpc/include/asm/kvm_book3s_64.h
>> @@ -148,7 +148,7 @@ static inline unsigned long compute_tlbie_rb(unsigned long v, unsigned long r,
>>  	/* This covers 14..54 bits of va*/
>>  	rb = (v & ~0x7fUL) << 16;		/* AVA field */
>>  
>> -	rb |= v >> (62 - 8);			/*  B field */
>> +	rb |= (v >> HPTE_V_SSIZE_SHIFT) << 8;	/*  B field */

or should we do. I guess the below is more closer to what we have in
rest of the code ?

       rb |= ((v >> (HPTE_V_SSIZE_SHIFT - 8)) & ~0xffUL); 


>>  	/*
>>  	 * AVA in v had cleared lower 23 bits. We need to derive
>>  	 * that from pteg index
>> -- 
>> 2.1.1
>>
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