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

From: Fabiano Rosas <farosas@linux.ibm.com>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: Michael Neuling <mikey@neuling.org>,
	linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org,
	Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH] KVM: PPC: Book3S HV: Save host FSCR in the P7/8 path
Date: Mon, 24 May 2021 09:49:46 -0300	[thread overview]
Message-ID: <87fsyc1el1.fsf@linux.ibm.com> (raw)
In-Reply-To: <20210523122101.3247232-1-npiggin@gmail.com>

Nicholas Piggin <npiggin@gmail.com> writes:

> 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 */
>  
>  /*
>   * Call kvmppc_hv_entry in real mode.
> @@ -686,6 +687,8 @@ BEGIN_FTR_SECTION
>  	std	r6, STACK_SLOT_DAWR0(r1)
>  	std	r7, STACK_SLOT_DAWRX0(r1)
>  	std	r8, STACK_SLOT_IAMR(r1)
> +	mfspr	r5, SPRN_FSCR
> +	std	r5, STACK_SLOT_FSCR(r1)
>  END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
>  BEGIN_FTR_SECTION
>  	mfspr	r6, SPRN_DAWR1
> @@ -1663,6 +1666,10 @@ FTR_SECTION_ELSE
>  	ld	r7, STACK_SLOT_HFSCR(r1)
>  	mtspr	SPRN_HFSCR, r7
>  ALT_FTR_SECTION_END_IFCLR(CPU_FTR_ARCH_300)
> +BEGIN_FTR_SECTION
> +	ld	r5, STACK_SLOT_FSCR(r1)
> +	mtspr	SPRN_FSCR, r5
> +END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
>  	/*
>  	 * Restore various registers to 0, where non-zero values
>  	 * set by the guest could disrupt the host.

So it seems this line in kvmppc_vcpu_run_hv loses its purpose now?

        do{
        (...)
	} while (is_kvmppc_resume_guest(r));

        /* Restore userspace EBB and other register values */
        if (cpu_has_feature(CPU_FTR_ARCH_207S)) {
                mtspr(SPRN_EBBHR, ebb_regs[0]);
                mtspr(SPRN_EBBRR, ebb_regs[1]);
                mtspr(SPRN_BESCR, ebb_regs[2]);
                mtspr(SPRN_TAR, user_tar);
--->            mtspr(SPRN_FSCR, current->thread.fscr);
        }