Messages in this thread | | | Date | Wed, 29 Jul 2015 12:25:58 +0100 | From | Julien Grall <> | Subject | Re: [PATCH 4/8] xen: Use the correctly the Xen memory terminologies |
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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); }
Similar splitting would be done for gfn_to_pfn and mfn_to_pfn.
Regards,
-- Julien Grall
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