netdev - RE: [PATCH net-next] net: mana: Add support for variable page sizes of ARM64

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Date: Tue, 11 Jun 2024 18:03:31 +0000
From: Haiyang Zhang <haiyangz@...rosoft.com>
To: Haiyang Zhang <haiyangz@...rosoft.com>, Michael Kelley
	<mhklinux@...look.com>, "linux-hyperv@...r.kernel.org"
	<linux-hyperv@...r.kernel.org>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, Paul Rosswurm <paulros@...rosoft.com>
CC: Dexuan Cui <decui@...rosoft.com>, "stephen@...workplumber.org"
	<stephen@...workplumber.org>, KY Srinivasan <kys@...rosoft.com>,
	"olaf@...fle.de" <olaf@...fle.de>, vkuznets <vkuznets@...hat.com>,
	"davem@...emloft.net" <davem@...emloft.net>, "wei.liu@...nel.org"
	<wei.liu@...nel.org>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
	"leon@...nel.org" <leon@...nel.org>, Long Li <longli@...rosoft.com>,
	"ssengar@...ux.microsoft.com" <ssengar@...ux.microsoft.com>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	"daniel@...earbox.net" <daniel@...earbox.net>, "john.fastabend@...il.com"
	<john.fastabend@...il.com>, "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
	"ast@...nel.org" <ast@...nel.org>, "hawk@...nel.org" <hawk@...nel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>, "shradhagupta@...ux.microsoft.com"
	<shradhagupta@...ux.microsoft.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net-next] net: mana: Add support for variable page sizes
 of ARM64



> -----Original Message-----
> From: Haiyang Zhang <haiyangz@...rosoft.com>
> Sent: Tuesday, June 11, 2024 1:44 PM
> To: Michael Kelley <mhklinux@...look.com>; linux-hyperv@...r.kernel.org;
> netdev@...r.kernel.org; Paul Rosswurm <paulros@...rosoft.com>
> Cc: Dexuan Cui <decui@...rosoft.com>; stephen@...workplumber.org; KY
> Srinivasan <kys@...rosoft.com>; olaf@...fle.de; vkuznets
> <vkuznets@...hat.com>; davem@...emloft.net; wei.liu@...nel.org;
> edumazet@...gle.com; kuba@...nel.org; pabeni@...hat.com; leon@...nel.org;
> Long Li <longli@...rosoft.com>; ssengar@...ux.microsoft.com; linux-
> rdma@...r.kernel.org; daniel@...earbox.net; john.fastabend@...il.com;
> bpf@...r.kernel.org; ast@...nel.org; hawk@...nel.org; tglx@...utronix.de;
> shradhagupta@...ux.microsoft.com; linux-kernel@...r.kernel.org
> Subject: RE: [PATCH net-next] net: mana: Add support for variable page
> sizes of ARM64


> > > @@ -183,7 +184,7 @@ int mana_smc_setup_hwc(struct shm_channel *sc,
> bool
> > > reset_vf, u64 eq_addr,
> > >
> > >  /* EQ addr: low 48 bits of frame address */
> > >  shmem = (u64 *)ptr;
> > > - frame_addr = PHYS_PFN(eq_addr);
> > > + frame_addr = MANA_PFN(eq_addr);
> > >  *shmem = frame_addr & PAGE_FRAME_L48_MASK;
> > >  all_addr_h4bits |= (frame_addr >> PAGE_FRAME_L48_WIDTH_BITS) <<
> > >         (frame_addr_seq++ * PAGE_FRAME_H4_WIDTH_BITS);
> >
> > In mana_smc_setup_hwc() a few lines above this change, code using
> > PAGE_ALIGNED() is unchanged.  Is it correct that the eq/cq/rq/sq
> > addresses
> > must be aligned to 64K if PAGE_SIZE is 64K?
> 
> Since we still using PHYS_PFN on them, if not aligned to PAGE_SIZE,
> the lower bits may be lost. (You said the same below.)
> 
> >
> > Related, I wonder about how MANA_PFN() is defined. If PAGE_SIZE is 64K,
> > MANA_PFN() will first right-shift 16, then left shift 4. The net is
> > right-shift 12,
> > corresponding to the 4K chunks that MANA expects. But that approach
> > guarantees
> > that the rightmost 4 bits of the MANA PFN will always be zero. That's
> > consistent
> > with requiring the addresses to be PAGE_ALIGNED() to 64K, but I'm
> unclear
> > whether
> > that is really the requirement. You might compare with the definition
> of
> > HVPFN_DOWN(), which has a similar goal for Linux guests communicating
> > with
> > Hyper-V.
> 
> @Paul Rosswurm You said MANA HW has "no page concept". So the
> "frame_addr"
> In the mana_smc_setup_hwc() is NOT related to physical page number,
> correct?
> Can we just use phys_adr >> 12 like below?
> 
> #define MANA_MIN_QSHIFT 12
> #define MANA_PFN(a) ((a) >> MANA_MIN_QSHIFT)
> 
>       /* EQ addr: low 48 bits of frame address */
>      shmem = (u64 *)ptr;
> -     frame_addr = PHYS_PFN(eq_addr);
> +     frame_addr = MANA_PFN(eq_addr);
> 

I just confirmed with Paul, we can use phys_adr >> 12.
And I will change the alignment requirements to be 4k.

Thanks,
- Haiyang