On 24.07.2025 13:04, Roger Pau Monne wrote: > There are four performance critical PDX conversion helpers that do the PFN > to/from PDX and the physical addresses to/from directmap offsets > translations. > > In the absence of an active PDX compression, those functions would still do > the calculations needed, just to return the same input value as no > translation is in place and hence PFN and PDX spaces are identity mapped. > > To reduce the overhead of having to do the pointless calculations allow > architectures to implement the translation helpers in a per-arch header. > Rename the existing conversion functions to add a trailing _xlate suffix, > so that the per-arch headers can define the non suffixed versions. > > Currently only x86 implements meaningful custom handlers to short circuit > the translation when not active, using asm goto. Other architectures use a > generic header that maps the non-xlate to the xlate variants to keep the > previous behavior. > > Signed-off-by: Roger Pau Monné <roger....@citrix.com>
Reviewed-by: Jan Beulich <jbeul...@suse.com> > --- /dev/null > +++ b/xen/arch/x86/include/asm/pdx.h > @@ -0,0 +1,75 @@ > +/* SPDX-License-Identifier: GPL-2.0-only */ > + > +#ifndef X86_PDX_H > +#define X86_PDX_H > + > +#ifndef CONFIG_PDX_NONE > + > +#include <asm/alternative.h> > + > +/* > + * Introduce a macro to avoid repeating the same asm goto block in each > helper. > + * Note the macro is strictly tied to the code in the helpers. > + */ > +#define PDX_ASM_GOTO(label) \ > + asm_inline goto ( \ > + ALTERNATIVE( \ > + "", \ > + "jmp %l0", \ > + ALT_NOT(X86_FEATURE_PDX_COMPRESSION)) \ > + : : : : label ) Considering the uses of the macro, it seems likely that in some of the cases the label will be within reach of a short JMP (opcode 0xEB), while the assembler will be unable to encode it like that (for living in a separate section, far off from the place the code will be copied to). That's likely okay for now, but we may want to eliminate this minor ineffeciency later on. Jan
