Re: [PATCH 0/3] powerpc/mm: Conditionally call H_BLOCK_REMOVE

[Laurent Dufour]

Le 12/09/2019 Ã 15:44, Aneesh Kumar K.V a ÃcritÂ:
> On 8/30/19 5:37 PM, Laurent Dufour wrote:
> > Since the commit ba2dd8a26baa ("powerpc/pseries/mm: call H_BLOCK_REMOVE"),
> > the call to H_BLOCK_REMOVE is always done if the feature is exhibited.
> >
> > On some system, the hypervisor may not support all the combination of
> > segment base page size and page size. When this happens the hcall is
> > returning H_PARAM, which is triggering a BUG_ON check leading to a panic.
> >
> > The PAPR document is specifying a TLB Block Invalidate Characteristics item
> > detailing which couple base page size, page size the hypervisor is
> > supporting through H_BLOCK_REMOVE. Furthermore, the characteristics are
> > also providing the size of the block the hcall could process.
> >
> > Supporting various block size seems not needed as all systems I was able to
> > play with was support an 8 addresses block size, which is the maximum
> > through the hcall. Supporting various size may complexify the algorithm in
> > call_block_remove() so unless this is required, this is not done.
> >
> > In the case of block size different from 8, a warning message is displayed
> > at boot time and that block size will be ignored checking for the
> > H_BLOCK_REMOVE support.
> >
> > Due to the minimal amount of hardware showing a limited set of
> > H_BLOCK_REMOVE supported page size, I don't think there is a need to push
> > this series to the stable mailing list.
> >
> > The first patch is initializing the penc values for each page size to an
> > invalid value to be able to detect those which have been initialized as 0
> > is a valid value.
> >
> > The second patch is reading the characteristic through the hcall
> > ibm,get-system-parameter and record the supported block size for each page
> > size.
> >
> > The third patch is changing the check used to detect the H_BLOCK_REMOVE
> > availability to take care of the base page size and page size couple.
>
> So ibm,segment-page-sizes indicates wether we support a combination of base 
> page size and actual page size. You are suggesting that the value reported 
> by that is not correct? Can you also share the early part of dmesg as below.

I'm not saying that the value reported by ibm,segment-page-sizes are 
incorrect, I'm saying that some couple are not supported by the hcall 
H_BLOCK_REMOVE.

May be should I change the second sentence by

On some system, the hypervisor may not support all the combination of 
segment base page size and page size for the hcall H_BLOCK_REMOVE. When 
this happens the hcall is returning H_PARAM, which is triggering a BUG_ON 
check leading to a panic.

Is that clear enough now ?

> [ÂÂÂ 0.000000] hash-mmu: Page sizes from device-tree:
> [ÂÂÂ 0.000000] hash-mmu: base_shift=12: shift=12, sllp=0x0000, 
> avpnm=0x00000000, tlbiel=1, penc=0
> [ÂÂÂ 0.000000] hash-mmu: base_shift=12: shift=16, sllp=0x0000, 
> avpnm=0x00000000, tlbiel=1, penc=7
> [ÂÂÂ 0.000000] hash-mmu: base_shift=12: shift=24, sllp=0x0000, 
> avpnm=0x00000000, tlbiel=1, penc=56
> [ÂÂÂ 0.000000] hash-mmu: base_shift=16: shift=16, sllp=0x0110, 
> avpnm=0x00000000, tlbiel=1, penc=1
> [ÂÂÂ 0.000000] hash-mmu: base_shift=16: shift=24, sllp=0x0110, 
> avpnm=0x00000000, tlbiel=1, penc=8
> [ÂÂÂ 0.000000] hash-mmu: base_shift=24: shift=24, sllp=0x0100, 
> avpnm=0x00000001, tlbiel=0, penc=0
> [ÂÂÂ 0.000000] hash-mmu: base_shift=34: shift=34, sllp=0x0120, 
> avpnm=0x000007ff, tlbiel=0, penc=3
>
> That shows different base page size and actual page size combination.
>
>
> > Laurent Dufour (3):
> > ÂÂ powerpc/mm: Initialize the HPTE encoding values
> > ÂÂ powperc/mm: read TLB Block Invalidate Characteristics
> > ÂÂ powerpc/mm: call H_BLOCK_REMOVE when supported
> >
> > Â arch/powerpc/include/asm/book3s/64/mmu.h |ÂÂ 3 +
> > Â arch/powerpc/mm/book3s64/hash_utils.cÂÂÂ |ÂÂ 8 +-
> > Â arch/powerpc/platforms/pseries/lpar.cÂÂÂ | 118 ++++++++++++++++++++++-
> > Â 3 files changed, 125 insertions(+), 4 deletions(-)
>
>
> -aneesh