From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@lst.de>
Date: Fri, 06 Sep 2019 16:32:41 +0000
Subject: Re: [PATCH v7 1/7] kvmppc: Driver to manage pages of secure guest
Message-Id: <20190906163241.GA12516@lst.de>
List-Id: <kvm-ppc.vger.kernel.org>
References: <20190822102620.21897-1-bharata@linux.ibm.com> <20190822102620.21897-2-bharata@linux.ibm.com> <20190829083810.GA13039@lst.de> <20190830034259.GD31913@in.ibm.com> <20190902075356.GA28967@lst.de> <20190906113639.GA8748@in.ibm.com>
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To: Bharata B Rao <bharata@linux.ibm.com>
Cc: Christoph Hellwig <hch@lst.de>, linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org, linux-mm@kvack.org, paulus@au1.ibm.com, aneesh.kumar@linux.vnet.ibm.com, jglisse@redhat.com, linuxram@us.ibm.com, sukadev@linux.vnet.ibm.com, cclaudio@linux.ibm.com

On Fri, Sep 06, 2019 at 05:06:39PM +0530, Bharata B Rao wrote:
> > Also is bit 56+ a set of values, so is there 1 << 56 and 3 << 56 as well?  Seems
> > like even that other patch doesn't fully define these "pfn" values.
> 
> I realized that the bit numbers have changed, it is no longer bits 60:56,
> but instead top 8bits. 
> 
> #define KVMPPC_RMAP_UVMEM_PFN   0x0200000000000000
> static inline bool kvmppc_rmap_is_uvmem_pfn(unsigned long *rmap)
> {
>         return ((*rmap & 0xff00000000000000) = KVMPPC_RMAP_UVMEM_PFN);
> }

In that overall scheme I'd actually much prefer something like (names
just made up, they should vaguely match the spec this written to):

static inline unsigned long kvmppc_rmap_type(unsigned long *rmap)
{
	return (rmap & 0xff00000000000000);
}

And then where you check it you can use:

	if (kvmppc_rmap_type(*rmap) = KVMPPC_RMAP_UVMEM_PFN)

and where you set it you do:

	*rmap |= KVMPPC_RMAP_UVMEM_PFN;

as in the current patch to keep things symmetric.