linux/arch/arm/kvm/init.S
Marc Zyngier 5a677ce044 ARM: KVM: switch to a dual-step HYP init code
Our HYP init code suffers from two major design issues:
- it cannot support CPU hotplug, as we tear down the idmap very early
- it cannot perform a TLB invalidation when switching from init to
  runtime mappings, as pages are manipulated from PL1 exclusively

The hotplug problem mandates that we keep two sets of page tables
(boot and runtime). The TLB problem mandates that we're able to
transition from one PGD to another while in HYP, invalidating the TLBs
in the process.

To be able to do this, we need to share a page between the two page
tables. A page that will have the same VA in both configurations. All we
need is a VA that has the following properties:
- This VA can't be used to represent a kernel mapping.
- This VA will not conflict with the physical address of the kernel text

The vectors page seems to satisfy this requirement:
- The kernel never maps anything else there
- The kernel text being copied at the beginning of the physical memory,
  it is unlikely to use the last 64kB (I doubt we'll ever support KVM
  on a system with something like 4MB of RAM, but patches are very
  welcome).

Let's call this VA the trampoline VA.

Now, we map our init page at 3 locations:
- idmap in the boot pgd
- trampoline VA in the boot pgd
- trampoline VA in the runtime pgd

The init scenario is now the following:
- We jump in HYP with four parameters: boot HYP pgd, runtime HYP pgd,
  runtime stack, runtime vectors
- Enable the MMU with the boot pgd
- Jump to a target into the trampoline page (remember, this is the same
  physical page!)
- Now switch to the runtime pgd (same VA, and still the same physical
  page!)
- Invalidate TLBs
- Set stack and vectors
- Profit! (or eret, if you only care about the code).

Note that we keep the boot mapping permanently (it is not strictly an
idmap anymore) to allow for CPU hotplug in later patches.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@cs.columbia.edu>
2013-04-28 22:23:10 -07:00

155 lines
4.3 KiB
ArmAsm

/*
* Copyright (C) 2012 - Virtual Open Systems and Columbia University
* Author: Christoffer Dall <c.dall@virtualopensystems.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License, version 2, as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#include <linux/linkage.h>
#include <asm/unified.h>
#include <asm/asm-offsets.h>
#include <asm/kvm_asm.h>
#include <asm/kvm_arm.h>
#include <asm/kvm_mmu.h>
/********************************************************************
* Hypervisor initialization
* - should be called with:
* r0 = top of Hyp stack (kernel VA)
* r1 = pointer to hyp vectors
* r2,r3 = Hypervisor pgd pointer
*
* The init scenario is:
* - We jump in HYP with four parameters: boot HYP pgd, runtime HYP pgd,
* runtime stack, runtime vectors
* - Enable the MMU with the boot pgd
* - Jump to a target into the trampoline page (remember, this is the same
* physical page!)
* - Now switch to the runtime pgd (same VA, and still the same physical
* page!)
* - Invalidate TLBs
* - Set stack and vectors
* - Profit! (or eret, if you only care about the code).
*
* As we only have four registers available to pass parameters (and we
* need six), we split the init in two phases:
* - Phase 1: r0 = 0, r1 = 0, r2,r3 contain the boot PGD.
* Provides the basic HYP init, and enable the MMU.
* - Phase 2: r0 = ToS, r1 = vectors, r2,r3 contain the runtime PGD.
* Switches to the runtime PGD, set stack and vectors.
*/
.text
.pushsection .hyp.idmap.text,"ax"
.align 5
__kvm_hyp_init:
.globl __kvm_hyp_init
@ Hyp-mode exception vector
W(b) .
W(b) .
W(b) .
W(b) .
W(b) .
W(b) __do_hyp_init
W(b) .
W(b) .
__do_hyp_init:
cmp r0, #0 @ We have a SP?
bne phase2 @ Yes, second stage init
@ Set the HTTBR to point to the hypervisor PGD pointer passed
mcrr p15, 4, r2, r3, c2
@ Set the HTCR and VTCR to the same shareability and cacheability
@ settings as the non-secure TTBCR and with T0SZ == 0.
mrc p15, 4, r0, c2, c0, 2 @ HTCR
ldr r2, =HTCR_MASK
bic r0, r0, r2
mrc p15, 0, r1, c2, c0, 2 @ TTBCR
and r1, r1, #(HTCR_MASK & ~TTBCR_T0SZ)
orr r0, r0, r1
mcr p15, 4, r0, c2, c0, 2 @ HTCR
mrc p15, 4, r1, c2, c1, 2 @ VTCR
ldr r2, =VTCR_MASK
bic r1, r1, r2
bic r0, r0, #(~VTCR_HTCR_SH) @ clear non-reusable HTCR bits
orr r1, r0, r1
orr r1, r1, #(KVM_VTCR_SL0 | KVM_VTCR_T0SZ | KVM_VTCR_S)
mcr p15, 4, r1, c2, c1, 2 @ VTCR
@ Use the same memory attributes for hyp. accesses as the kernel
@ (copy MAIRx ro HMAIRx).
mrc p15, 0, r0, c10, c2, 0
mcr p15, 4, r0, c10, c2, 0
mrc p15, 0, r0, c10, c2, 1
mcr p15, 4, r0, c10, c2, 1
@ Set the HSCTLR to:
@ - ARM/THUMB exceptions: Kernel config (Thumb-2 kernel)
@ - Endianness: Kernel config
@ - Fast Interrupt Features: Kernel config
@ - Write permission implies XN: disabled
@ - Instruction cache: enabled
@ - Data/Unified cache: enabled
@ - Memory alignment checks: enabled
@ - MMU: enabled (this code must be run from an identity mapping)
mrc p15, 4, r0, c1, c0, 0 @ HSCR
ldr r2, =HSCTLR_MASK
bic r0, r0, r2
mrc p15, 0, r1, c1, c0, 0 @ SCTLR
ldr r2, =(HSCTLR_EE | HSCTLR_FI | HSCTLR_I | HSCTLR_C)
and r1, r1, r2
ARM( ldr r2, =(HSCTLR_M | HSCTLR_A) )
THUMB( ldr r2, =(HSCTLR_M | HSCTLR_A | HSCTLR_TE) )
orr r1, r1, r2
orr r0, r0, r1
isb
mcr p15, 4, r0, c1, c0, 0 @ HSCR
@ End of init phase-1
eret
phase2:
@ Set stack pointer
mov sp, r0
@ Set HVBAR to point to the HYP vectors
mcr p15, 4, r1, c12, c0, 0 @ HVBAR
@ Jump to the trampoline page
ldr r0, =TRAMPOLINE_VA
adr r1, target
bfi r0, r1, #0, #PAGE_SHIFT
mov pc, r0
target: @ We're now in the trampoline code, switch page tables
mcrr p15, 4, r2, r3, c2
isb
@ Invalidate the old TLBs
mcr p15, 4, r0, c8, c7, 0 @ TLBIALLH
dsb
eret
.ltorg
.globl __kvm_hyp_init_end
__kvm_hyp_init_end:
.popsection