linux-kernel - Re: [PATCH v3 0/3] Off-load TLB invalidations to host for !GTSE

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Date:   Fri, 17 Jul 2020 09:58:54 +0530
From:   Bharata B Rao <bharata@...ux.ibm.com>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     Qian Cai <cai@....pw>, aneesh.kumar@...ux.ibm.com,
        linux-kernel@...r.kernel.org, linux-next@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, mpe@...erman.id.au,
        sfr@...b.auug.org.au
Subject: Re: [PATCH v3 0/3] Off-load TLB invalidations to host for !GTSE

On Fri, Jul 17, 2020 at 12:44:00PM +1000, Nicholas Piggin wrote:
> Excerpts from Nicholas Piggin's message of July 17, 2020 12:08 pm:
> > Excerpts from Qian Cai's message of July 17, 2020 3:27 am:
> >> On Fri, Jul 03, 2020 at 11:06:05AM +0530, Bharata B Rao wrote:
> >>> Hypervisor may choose not to enable Guest Translation Shootdown Enable
> >>> (GTSE) option for the guest. When GTSE isn't ON, the guest OS isn't
> >>> permitted to use instructions like tblie and tlbsync directly, but is
> >>> expected to make hypervisor calls to get the TLB flushed.
> >>> 
> >>> This series enables the TLB flush routines in the radix code to
> >>> off-load TLB flushing to hypervisor via the newly proposed hcall
> >>> H_RPT_INVALIDATE. 
> >>> 
> >>> To easily check the availability of GTSE, it is made an MMU feature.
> >>> The OV5 handling and H_REGISTER_PROC_TBL hcall are changed to
> >>> handle GTSE as an optionally available feature and to not assume GTSE
> >>> when radix support is available.
> >>> 
> >>> The actual hcall implementation for KVM isn't included in this
> >>> patchset and will be posted separately.
> >>> 
> >>> Changes in v3
> >>> =============
> >>> - Fixed a bug in the hcall wrapper code where we were missing setting
> >>>   H_RPTI_TYPE_NESTED while retrying the failed flush request with
> >>>   a full flush for the nested case.
> >>> - s/psize_to_h_rpti/psize_to_rpti_pgsize
> >>> 
> >>> v2: https://lore.kernel.org/linuxppc-dev/20200626131000.5207-1-bharata@linux.ibm.com/T/#t
> >>> 
> >>> Bharata B Rao (2):
> >>>   powerpc/mm: Enable radix GTSE only if supported.
> >>>   powerpc/pseries: H_REGISTER_PROC_TBL should ask for GTSE only if
> >>>     enabled
> >>> 
> >>> Nicholas Piggin (1):
> >>>   powerpc/mm/book3s64/radix: Off-load TLB invalidations to host when
> >>>     !GTSE
> >> 
> >> Reverting the whole series fixed random memory corruptions during boot on
> >> POWER9 PowerNV systems below.
> > 
> > If I s/mmu_has_feature(MMU_FTR_GTSE)/(1)/g in radix_tlb.c, then the .o
> > disasm is the same as reverting my patch.
> > 
> > Feature bits not being set right? PowerNV should be pretty simple, seems
> > to do the same as FTR_TYPE_RADIX.
> 
> Might need this fix
> 
> ---
> 
> diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
> index 9cc49f265c86..54c9bcea9d4e 100644
> --- a/arch/powerpc/kernel/prom.c
> +++ b/arch/powerpc/kernel/prom.c
> @@ -163,7 +163,7 @@ static struct ibm_pa_feature {
>  	{ .pabyte = 0,  .pabit = 6, .cpu_features  = CPU_FTR_NOEXECUTE },
>  	{ .pabyte = 1,  .pabit = 2, .mmu_features  = MMU_FTR_CI_LARGE_PAGE },
>  #ifdef CONFIG_PPC_RADIX_MMU
> -	{ .pabyte = 40, .pabit = 0, .mmu_features  = MMU_FTR_TYPE_RADIX },
> +	{ .pabyte = 40, .pabit = 0, .mmu_features  = (MMU_FTR_TYPE_RADIX | MMU_FTR_GTSE) },
>  #endif
>  	{ .pabyte = 1,  .pabit = 1, .invert = 1, .cpu_features = CPU_FTR_NODSISRALIGN },
>  	{ .pabyte = 5,  .pabit = 0, .cpu_features  = CPU_FTR_REAL_LE,

Michael - Let me know if this should be folded into 1/3 and the complete
series resent.

Regards,
Bharata.