Re: [Qemu-ppc] Power9 VRMA emulation

[David Gibson]

On Sat, May 18, 2019 at 10:47:22AM +0530, Amol Surati wrote:
> Hello again,
> 
> 
> A bit of testing was carried out.
> 
> 
> 
> As it is now, qemu raises a HISI without consulting the VRMA SLB and the
> partitions page table.
> 
> This is the message it prints for when a (non-zero LPIDR) partition was made
> to run under VRMA (for an arbitrary instruction address 0x8ee8):
> 
> "Raise exception at 0000000000008ee8 => 00000046 (8000000)"
> The error code 8000000 is SRR1_PROTFAULT.
> 
> 
> 
> After allowing LPCR_VPM0 as a valid bit for POWERPC_MMU_3_00, and setting
> it to 1, the above test was repeated. This is the output:
> 
> htab_base 0000000000000000 htab_mask 00000000000007ff hash 0003fffffffffff7
> 0 htab=0000000000000000/00000000000007ff vsid=0000000001ffffff
> ptem=4001ffffff000001 hash=0003fffffffffff7
> 1 htab=0000000000000000/00000000000007ff vsid=0000000001ffffff
> api=4001ffffff000003 hash=fffc000000000008
> Raise exception at 0000000000008ee8 => 00000046 (40000000)
> 
> The error code 40000000 is SRR1_NOPTE. That code and qemu's attempt to
> search in the page table for the partition, correspond with the comment
> in the ISA that HISI is to be raised only when (1) VPM is ON and (2)
> conditions exist which warrant raising a ISI/DSI.
> 
> IIURC, the conditions which warrant raising a storage interrupt are those
> which correspond to failure in translating VA to RA (i.e. failure in
> finding a valid PTE, assuming TLB was empty).
> 
> 
> 
> 
> QEMU seems to ignore that bit of ISA and raises the HISI (in the above
> test) without checking the page table. Instead of removing LPCR_VPM0 bit
> for POWERPC_MMU_3_00, qemu should consider that bit as 1 for all
> purposes except for the display purpose.
> 
> Does that make sense, or am I misinterpreting the ISA?

Which version of qemu are you using?  I quite recently merged a bunch
of patches from Suraj which make a number of fixes to TCG's HV mode
implementation.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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