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Date: Fri, 6 Sep 2019 18:32:41 +0200
From: Christoph Hellwig <hch@lst.de>
To: Bharata B Rao <bharata@linux.ibm.com>
Subject: Re: [PATCH v7 1/7] kvmppc: Driver to manage pages of secure guest
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Cc: linuxram@us.ibm.com, cclaudio@linux.ibm.com, kvm-ppc@vger.kernel.org,
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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.