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Instead help CSE (when MEM_SHARING=y) by introducing a local variable holding the page owner. Signed-off-by: Jan Beulich --- According to my observations gcc12 manages to CSE mfn_to_page() but not (all of) page_get_owner(). The overall savings there are, partly due to knock-on effects, 64 bytes of code. While looking there, "mfn_eq(omfn, mfn_add(mfn, i))" near the end of the same loop caught my eye: Is that really correct? Shouldn't we fail the operation if the MFN which "ogfn" was derived from doesn't match the MFN "ogfn" maps to? Excluding grant mappings here is of course okay, but that's already taken care of by the enclosing p2m_is_ram(). --- a/xen/arch/x86/mm/p2m.c +++ b/xen/arch/x86/mm/p2m.c @@ -691,8 +691,10 @@ p2m_add_page(struct domain *d, gfn_t gfn /* Then, look for m->p mappings for this range and deal with them */ for ( i = 0; i < (1UL << page_order); i++ ) { - if ( dom_cow && - page_get_owner(mfn_to_page(mfn_add(mfn, i))) == dom_cow ) + const struct domain *owner = + page_get_owner(mfn_to_page(mfn_add(mfn, i))); + + if ( dom_cow && owner == dom_cow ) { /* This is no way to add a shared page to your physmap! */ gdprintk(XENLOG_ERR, "Adding shared mfn %lx directly to dom%d physmap not allowed.\n", @@ -700,7 +702,7 @@ p2m_add_page(struct domain *d, gfn_t gfn p2m_unlock(p2m); return -EINVAL; } - if ( page_get_owner(mfn_to_page(mfn_add(mfn, i))) != d ) + if ( owner != d ) continue; ogfn = mfn_to_gfn(d, mfn_add(mfn, i)); if ( !gfn_eq(ogfn, _gfn(INVALID_M2P_ENTRY)) &&