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

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

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