Messages in this thread | | | Date | Wed, 29 Jul 2015 10:14:47 -0400 | From | Boris Ostrovsky <> | Subject | Re: [PATCH 4/8] xen: Use the correctly the Xen memory terminologies |
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On 07/29/2015 07:25 AM, Julien Grall wrote: > Hi Boris, > > On 28/07/15 20:12, Boris Ostrovsky wrote: >> On 07/28/2015 11:02 AM, Julien Grall wrote: >>> Based on include/xen/mm.h [1], Linux is mistakenly using MFN when GFN >>> is meant, I suspect this is because the first support for Xen was for >>> PV. This brough some misimplementation of helpers on ARM and make the >>> developper confused the expected behavior. >>> >>> For instance, with pfn_to_mfn, we expect to get an MFN based on the name. >>> Although, if we look at the implementation on x86, it's returning a GFN. >>> >>> For clarity and avoid new confusion, replace any reference of mfn into >>> gnf in any helpers used by PV drivers. >> >> >> >> >>> @@ -730,7 +730,7 @@ static void xen_do_pin(unsigned level, unsigned >>> long pfn) >>> struct mmuext_op op; >>> >>> op.cmd = level; >>> - op.arg1.mfn = pfn_to_mfn(pfn); >>> + op.arg1.mfn = pfn_to_gfn(pfn); >> >> >> This looks slightly odd. It is correct but given that purpose of this >> series is to make things more clear perhaps we can add another union >> member (gfn) to mmuext_op.arg1? >> >> (Of course, the hypervisor will continue referring to mfn which could >> still be confusing) > > This operation is only used for PV guests, right? > > IHMO re-introducing pfn_to_mfn for PV-guests only (i.e with a BUG_ON to > ensure no usage for auto-translated guest) would be the best solution. > It would avoid to have different name than the hypersivor one in the > hypercall interface. It will also make clear that virt_to_machine & co > is only PV specific. > > I though doing this but I preferred to defer it to x86 expert as my > knowledge for x86 Xen is very limited. I don't know where it's more > suitable to use MFN or GFN. I guess this file (mmu.c) is mostly PV specific? > > Would something like below fine for you? > > static inline unsigned long pfn_to_mfn(unsigned long pfn) > { > unsigned long mfn; > > BUG_ON(xen_feature(XENFEAT_auto_translated_physmap)); > > mfn = __pfn_to_mfn(pfn); > if (mfn != INVALID_P2M_ENTRY) > mfn &= ~(FOREIGN_FRAME_BIT | IDENTITY_FRAME_BIT); > > return mfn; > } > > static inline unsigned long pfn_to_gfn(unsigned long pfn) > { > if (xen_feature(XENFEAT_autotranslated_physmap)) > return pfn; > else > return pfn_to_mfn(pfn); > }
But you'd still say 'op.arg1.mfn = pfn_to_gfn(pfn);' in xen_do_pin() i.e. assign GFN to MFN, right? That's what I was referring to.
(In general, I am not sure a guest should ever use 'mfn' as it is purely a hypervisor construct. Including p2m, which I think should really be p2g as this is what we use to figure out what to stick into page tables)
-boris
> > Similar splitting would be done for gfn_to_pfn and mfn_to_pfn. > > Regards, >
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