arm64: allow kernel Image to be loaded anywhere in physical memory

This relaxes the kernel Image placement requirements, so that it
may be placed at any 2 MB aligned offset in physical memory.

This is accomplished by ignoring PHYS_OFFSET when installing
memblocks, and accounting for the apparent virtual offset of
the kernel Image. As a result, virtual address references
below PAGE_OFFSET are correctly mapped onto physical references
into the kernel Image regardless of where it sits in memory.

Special care needs to be taken for dealing with memory limits passed
via mem=, since the generic implementation clips memory top down, which
may clip the kernel image itself if it is loaded high up in memory. To
deal with this case, we simply add back the memory covering the kernel
image, which may result in more memory to be retained than was passed
as a mem= parameter.

Since mem= should not be considered a production feature, a panic notifier
handler is installed that dumps the memory limit at panic time if one was
set.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 1 insertions, 16 deletions

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 31b56008f412..054ac25e7c2e 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -26,24 +26,9 @@
 #define KVM_ARM64_DEBUG_DIRTY_SHIFT	0
 #define KVM_ARM64_DEBUG_DIRTY		(1 << KVM_ARM64_DEBUG_DIRTY_SHIFT)
 
-#define kvm_ksym_ref(sym)		((void *)&sym + kvm_ksym_shift)
+#define kvm_ksym_ref(sym)		phys_to_virt((u64)&sym - kimage_voffset)
 
 #ifndef __ASSEMBLY__
-#if __GNUC__ > 4
-#define kvm_ksym_shift			(PAGE_OFFSET - KIMAGE_VADDR)
-#else
-/*
- * GCC versions 4.9 and older will fold the constant below into the addend of
- * the reference to 'sym' above if kvm_ksym_shift is declared static or if the
- * constant is used directly. However, since we use the small code model for
- * the core kernel, the reference to 'sym' will be emitted as a adrp/add pair,
- * with a +/- 4 GB range, resulting in linker relocation errors if the shift
- * is sufficiently large. So prevent the compiler from folding the shift into
- * the addend, by making the shift a variable with external linkage.
- */
-__weak u64 kvm_ksym_shift = PAGE_OFFSET - KIMAGE_VADDR;
-#endif
-
 struct kvm;
 struct kvm_vcpu;