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Date: Tue, 29 Nov 2022 19:48:34 +1000
Message-Id: <COOOOI7S3TPI.1DW4KMM8NP70B@bobo>
Subject: Re: [PATCH v4 4/7] powerpc/64s: IOption for MSR stored in r12
From: "Nicholas Piggin" <npiggin@gmail.com>
To: "Rohan McLure" <rmclure@linux.ibm.com>, <linuxppc-dev@lists.ozlabs.org>
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References: <20221129044354.1836018-1-rmclure@linux.ibm.com>
 <20221129044354.1836018-4-rmclure@linux.ibm.com>
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On Tue Nov 29, 2022 at 2:43 PM AEST, Rohan McLure wrote:
> Interrupt handlers in asm/exceptions-64s.S contain a great deal of common
> code produced by the GEN_COMMON macros. Currently, at the exit point of
> the macro, r12 will contain the contents of the MSR. A future patch will
> cause these macros to zeroise architected registers to avoid potential
> speculation influence of user data.
>
> Provide an IOption that signals that r12 must be retained, as the
> interrupt handler assumes it to hold the contents of the MSR.

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

>
> Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
> ---
> v4: Split 64s register sanitisation commit to establish this IOption
> ---
>  arch/powerpc/kernel/exceptions-64s.S | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/e=
xceptions-64s.S
> index 5381a43e50fe..58d72db1d484 100644
> --- a/arch/powerpc/kernel/exceptions-64s.S
> +++ b/arch/powerpc/kernel/exceptions-64s.S
> @@ -111,6 +111,7 @@ name:
>  #define ISTACK		.L_ISTACK_\name\()	/* Set regular kernel stack */
>  #define __ISTACK(name)	.L_ISTACK_ ## name
>  #define IKUAP		.L_IKUAP_\name\()	/* Do KUAP lock */
> +#define IMSR_R12	.L_IMSR_R12_\name\()	/* Assumes MSR saved to r12 */
> =20
>  #define INT_DEFINE_BEGIN(n)						\
>  .macro int_define_ ## n name
> @@ -176,6 +177,9 @@ do_define_int n
>  	.ifndef IKUAP
>  		IKUAP=3D1
>  	.endif
> +	.ifndef IMSR_R12
> +		IMSR_R12=3D0
> +	.endif
>  .endm
> =20
>  /*
> @@ -1751,6 +1755,7 @@ INT_DEFINE_BEGIN(fp_unavailable)
>  #ifdef CONFIG_KVM_BOOK3S_PR_POSSIBLE
>  	IKVM_REAL=3D1
>  #endif
> +	IMSR_R12=3D1
>  INT_DEFINE_END(fp_unavailable)
> =20
>  EXC_REAL_BEGIN(fp_unavailable, 0x800, 0x100)
> @@ -2372,6 +2377,7 @@ INT_DEFINE_BEGIN(altivec_unavailable)
>  #ifdef CONFIG_KVM_BOOK3S_PR_POSSIBLE
>  	IKVM_REAL=3D1
>  #endif
> +	IMSR_R12=3D1
>  INT_DEFINE_END(altivec_unavailable)
> =20
>  EXC_REAL_BEGIN(altivec_unavailable, 0xf20, 0x20)
> @@ -2421,6 +2427,7 @@ INT_DEFINE_BEGIN(vsx_unavailable)
>  #ifdef CONFIG_KVM_BOOK3S_PR_POSSIBLE
>  	IKVM_REAL=3D1
>  #endif
> +	IMSR_R12=3D1
>  INT_DEFINE_END(vsx_unavailable)
> =20
>  EXC_REAL_BEGIN(vsx_unavailable, 0xf40, 0x20)
> --=20
> 2.37.2