[PATCH] KVM: PPC: Book3S HV: increase KVMPPC_NR_LPIDS on POWER8 and POWER9

[Cédric Le Goater]

On 6/8/20 1:57 PM, Cédric Le Goater wrote:
> POWER8 and POWER9 have 12-bit LPIDs. Change LPID_RSVD to support up to
> (4096 - 2) guests on these processors. POWER7 is kept the same with a
> limitation of (1024 - 2), but it might be time to drop KVM support for
> POWER7.
> 
> Tested with 2048 guests * 4 vCPUs on a witherspoon system with 512G
> RAM and a bit of swap.

For the record, it is possible to run 4094 guests * 4 vCPUs on a POWER9 
system with 1TB. It takes ~5m to boot them all.

CONFIG_NR_IRQS needs to be increased to support 4094 * 4 escalation 
interrupts.

Cheers,

C.


> 
> Signed-off-by: Cédric Le Goater <clg at kaod.org>
> ---
>  arch/powerpc/include/asm/reg.h      | 3 ++-
>  arch/powerpc/kvm/book3s_64_mmu_hv.c | 8 ++++++--
>  2 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
> index 88e6c78100d9..b70bbfb0ea3c 100644
> --- a/arch/powerpc/include/asm/reg.h
> +++ b/arch/powerpc/include/asm/reg.h
> @@ -473,7 +473,8 @@
>  #ifndef SPRN_LPID
>  #define SPRN_LPID	0x13F	/* Logical Partition Identifier */
>  #endif
> -#define   LPID_RSVD	0x3ff		/* Reserved LPID for partn switching */
> +#define   LPID_RSVD_POWER7	0x3ff	/* Reserved LPID for partn switching */
> +#define   LPID_RSVD		0xfff	/* Reserved LPID for partn switching */
>  #define	SPRN_HMER	0x150	/* Hypervisor maintenance exception reg */
>  #define   HMER_DEBUG_TRIG	(1ul << (63 - 17)) /* Debug trigger */
>  #define	SPRN_HMEER	0x151	/* Hyp maintenance exception enable reg */
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> index 18aed9775a3c..23035ab2ec50 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -260,11 +260,15 @@ int kvmppc_mmu_hv_init(void)
>  	if (!mmu_has_feature(MMU_FTR_LOCKLESS_TLBIE))
>  		return -EINVAL;
>  
> -	/* POWER7 has 10-bit LPIDs (12-bit in POWER8) */
>  	host_lpid = 0;
>  	if (cpu_has_feature(CPU_FTR_HVMODE))
>  		host_lpid = mfspr(SPRN_LPID);
> -	rsvd_lpid = LPID_RSVD;
> +
> +	/* POWER8 and above have 12-bit LPIDs (10-bit in POWER7) */
> +	if (cpu_has_feature(CPU_FTR_ARCH_207S))
> +		rsvd_lpid = LPID_RSVD;
> +	else
> +		rsvd_lpid = LPID_RSVD_POWER7;
>  
>  	kvmppc_init_lpid(rsvd_lpid + 1);
>  
>