[uaccess] Generalise librm's virt_offset mechanism for RISC-V

The virtual offset memory model used for i386-pcbios and x86_64-pcbios
can be generalised to also cover riscv32-sbi and riscv64-sbi.  In both
architectures, the 32-bit builds will use a circular map of the 32-bit
address space, and the 64-bit builds will use an identity map for the
relevant portion of the physical address space, with iPXE itself
placed in the negative (kernel) address space.

Generalise and document the virt_offset mechanism, and set it as the
default for both PCBIOS and SBI platforms.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/riscv/prefix/libprefix.S

@@ -41,6 +41,13 @@ prefix_virt:
 	.dword	_prefix
 	.size	prefix_virt, . - prefix_virt
 
+	/* Current virtual address offset */
+	.section ".data.virt_offset", "aw", @progbits
+	.globl	virt_offset
+virt_offset:
+	.space	( __riscv_xlen / 8 )
+	.size	virt_offset, . - virt_offset
+
 /*****************************************************************************
  *
  * Print message to debug console

src/arch/x86/image/elfboot.c

@@ -26,11 +26,11 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #include <string.h>
 #include <errno.h>
 #include <elf.h>
+#include <librm.h>
 #include <ipxe/image.h>
 #include <ipxe/elf.h>
 #include <ipxe/features.h>
 #include <ipxe/init.h>
-#include <ipxe/uaccess.h>
 
 /**
  * @file

src/arch/x86/include/bits/uaccess.h

@@ -1,14 +0,0 @@
-#ifndef _BITS_UACCESS_H
-#define _BITS_UACCESS_H
-
-/** @file
- *
- * x86-specific user access API implementations
- *
- */
-
-FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
-
-#include <librm.h>
-
-#endif /* _BITS_UACCESS_H */

src/arch/x86/include/librm.h

@@ -64,12 +64,6 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 #else /* ASSEMBLY */
 
-#ifdef UACCESS_LIBRM
-#define UACCESS_PREFIX_librm
-#else
-#define UACCESS_PREFIX_librm __librm_
-#endif
-
 /**
  * Call C function from real-mode code
  *
@@ -79,53 +73,6 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 	"pushl $( " _S2 ( VIRTUAL ( function ) ) " )\n\t"		\
 	"call virt_call\n\t"
 
-/* Variables in librm.S */
-extern const unsigned long virt_offset;
-
-/**
- * Convert physical address to user pointer
- *
- * @v phys		Physical address
- * @ret virt		Virtual address
- */
-static inline __always_inline void *
-UACCESS_INLINE ( librm, phys_to_virt ) ( unsigned long phys ) {
-
-	/* In a 64-bit build, any valid physical address is directly
-	 * usable as a virtual address, since the low 4GB is
-	 * identity-mapped.
-	 */
-	if ( sizeof ( physaddr_t ) > sizeof ( uint32_t ) )
-		return ( ( void * ) phys );
-
-	/* In a 32-bit build, subtract virt_offset */
-	return ( ( void * ) ( phys - virt_offset ) );
-}
-
-/**
- * Convert virtual address to physical address
- *
- * @v virt		Virtual address
- * @ret phys		Physical address
- */
-static inline __always_inline physaddr_t
-UACCESS_INLINE ( librm, virt_to_phys ) ( volatile const void *virt ) {
-	physaddr_t addr = ( ( physaddr_t ) virt );
-
-	/* In a 64-bit build, any virtual address in the low 4GB is
-	 * directly usable as a physical address, since the low 4GB is
-	 * identity-mapped.
-	 */
-	if ( ( sizeof ( physaddr_t ) > sizeof ( uint32_t ) ) &&
-	     ( addr <= 0xffffffffUL ) )
-		return addr;
-
-	/* In a 32-bit build or in a 64-bit build with a virtual
-	 * address above 4GB: add virt_offset
-	 */
-	return ( addr + virt_offset );
-}
-
 /******************************************************************************
  *
  * Access to variables in .data16 and .text16

src/arch/x86/include/realmode.h

@@ -4,6 +4,7 @@
 #include <stdint.h>
 #include <string.h>
 #include <registers.h>
+#include <librm.h>
 #include <ipxe/uaccess.h>
 
 /*

src/arch/x86/interface/pcbios/bios_mp.c

@@ -30,6 +30,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  */
 
 #include <registers.h>
+#include <librm.h>
 #include <ipxe/uaccess.h>
 #include <ipxe/timer.h>
 #include <ipxe/msr.h>

src/arch/x86/transitions/librm_mgmt.c

@@ -429,8 +429,6 @@ void setup_sipi ( unsigned int vector, uint32_t handler,
 	copy_to_real ( ( vector << 8 ), 0, sipi, ( ( size_t ) sipi_len ) );
 }
 
-PROVIDE_UACCESS_INLINE ( librm, phys_to_virt );
-PROVIDE_UACCESS_INLINE ( librm, virt_to_phys );
 PROVIDE_IOMAP_INLINE ( pages, io_to_bus );
 PROVIDE_IOMAP ( pages, ioremap, ioremap_pages );
 PROVIDE_IOMAP ( pages, iounmap, iounmap_pages );