Re: [PATCH] KVM: PPC: Book3S HV: Save host FSCR in the P7/8 path

[Nicholas Piggin <npiggin@gmail.com>]

Excerpts from Nicholas Piggin's message of May 23, 2021 10:21 pm:
> Similar to commit 25edcc50d76c ("KVM: PPC: Book3S HV: Save and restore
> FSCR in the P9 path"), ensure the P7/8 path saves and restores the host
> FSCR. The logic explained in that patch actually applies there to the
> old path well: a context switch can be made before kvmppc_vcpu_run_hv
> restores the host FSCR and returns.
> 
> Fixes: b005255e12a3 ("KVM: PPC: Book3S HV: Context-switch new POWER8 SPRs")
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  arch/powerpc/kvm/book3s_hv_rmhandlers.S | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> index 5e634db4809b..2b98e710c7a1 100644
> --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> @@ -44,7 +44,7 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_300)
>  #define NAPPING_UNSPLIT	3
>  
>  /* Stack frame offsets for kvmppc_hv_entry */
> -#define SFS			208
> +#define SFS			216
>  #define STACK_SLOT_TRAP		(SFS-4)
>  #define STACK_SLOT_SHORT_PATH	(SFS-8)
>  #define STACK_SLOT_TID		(SFS-16)
> @@ -59,8 +59,9 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_300)
>  #define STACK_SLOT_UAMOR	(SFS-88)
>  #define STACK_SLOT_DAWR1	(SFS-96)
>  #define STACK_SLOT_DAWRX1	(SFS-104)
> +#define STACK_SLOT_FSCR		(SFS-112)
>  /* the following is used by the P9 short path */
> -#define STACK_SLOT_NVGPRS	(SFS-152)	/* 18 gprs */
> +#define STACK_SLOT_NVGPRS	(SFS-160)	/* 18 gprs */

Actually, hmm.. this is wrong because nvgprs are subtracted from
this offset. But then I can't work out why 95a6432ce9038 raised
SFS from 160 to 208.

Thanks,
Nick