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KVM: arm64: add comments to __kern_hyp_va

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Document this function a little, to make it easier to understand.

The assembly comments were copied from the kern_hyp_va asm macro.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240208105422.3444159-2-joey.gouly@arm.com
[oliver: migrate a bit more detail from the asm variant]
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
This commit is contained in:
Joey Gouly 2024-02-08 10:54:21 +00:00 committed by Oliver Upton
parent 1f3ca7023f
commit d198e2668e
1 changed files with 20 additions and 10 deletions
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30
arch/arm64/include/asm/kvm_mmu.h
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@ -56,11 +56,6 @@
/*
* Convert a kernel VA into a HYP VA.
* reg: VA to be converted.
*
* The actual code generation takes place in kvm_update_va_mask, and
* the instructions below are only there to reserve the space and
* perform the register allocation (kvm_update_va_mask uses the
* specific registers encoded in the instructions).
*/
.macro kern_hyp_va reg
#ifndef __KVM_VHE_HYPERVISOR__
@ -127,14 +122,29 @@ void kvm_apply_hyp_relocations(void);
#define __hyp_pa(x) (((phys_addr_t)(x)) + hyp_physvirt_offset)
/*
* Convert a kernel VA into a HYP VA.
*
* Can be called from hyp or non-hyp context.
*
* The actual code generation takes place in kvm_update_va_mask(), and
* the instructions below are only there to reserve the space and
* perform the register allocation (kvm_update_va_mask() uses the
* specific registers encoded in the instructions).
*/
static __always_inline unsigned long __kern_hyp_va(unsigned long v)
{
/*
* This #ifndef is an optimisation for when this is called from VHE hyp
* context. When called from a VHE non-hyp context, kvm_update_va_mask() will
* replace the instructions with `nop`s.
*/
#ifndef __KVM_VHE_HYPERVISOR__
asm volatile(ALTERNATIVE_CB("and %0, %0, #1\n"
"ror %0, %0, #1\n"
"add %0, %0, #0\n"
"add %0, %0, #0, lsl 12\n"
"ror %0, %0, #63\n",
asm volatile(ALTERNATIVE_CB("and %0, %0, #1\n" /* mask with va_mask */
"ror %0, %0, #1\n" /* rotate to the first tag bit */
"add %0, %0, #0\n" /* insert the low 12 bits of the tag */
"add %0, %0, #0, lsl 12\n" /* insert the top 12 bits of the tag */
"ror %0, %0, #63\n", /* rotate back */
ARM64_ALWAYS_SYSTEM,
kvm_update_va_mask)
: "+r" (v));