[PATCH 04/23] arm64: kvm: Fix IDMAP overlap with HYP VA

Marc Zyngier
2020-01-30T13:26:15Z

From: Russell King <rmk+kernel@armlinux.org.uk>

Booting 5.4 on LX2160A reveals that KVM is non-functional:

kvm: Limiting the IPA size due to kernel Virtual Address limit
kvm [1]: IPA Size Limit: 43bits
kvm [1]: IDMAP intersecting with HYP VA, unable to continue
kvm [1]: error initializing Hyp mode: -22

Debugging shows:

kvm [1]: IDMAP page: 81a26000
kvm [1]: HYP VA range: 0:22ffffffff

as RAM is located at:

80000000-fbdfffff : System RAM
2080000000-237fffffff : System RAM

Comparing this with the same kernel on Armada 8040 shows:

kvm: Limiting the IPA size due to kernel Virtual Address limit
kvm [1]: IPA Size Limit: 43bits
kvm [1]: IDMAP page: 2a26000
kvm [1]: HYP VA range: 4800000000:493fffffff
...
kvm [1]: Hyp mode initialized successfully

which indicates that hyp_va_msb is set, and is always set to the
opposite value of the idmap page to avoid the overlap. This does not
happen with the LX2160A.

Further debugging shows vabits_actual = 39, kva_msb = 38 on LX2160A and
kva_msb = 33 on Armada 8040. Looking at the bit layout of the HYP VA,
there is still one bit available for hyp_va_msb. Set this bit
appropriately. This allows KVM to be functional on the LX2160A, but
without any HYP VA randomisation:

kvm: Limiting the IPA size due to kernel Virtual Address limit
kvm [1]: IPA Size Limit: 43bits
kvm [1]: IDMAP page: 81a24000
kvm [1]: HYP VA range: 4000000000:62ffffffff
...
kvm [1]: Hyp mode initialized successfully

Fixes: ed57cac83e05 ("arm64: KVM: Introduce EL2 VA randomisation")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
[maz: small additional cleanups, preserved case where the tag
is legitimately 0 and we can just use the mask, Fixes tag]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/E1ilAiY-0000MA-RG@rmk-PC.armlinux.org.uk
---
arch/arm64/kvm/va_layout.c | 56 +++++++++++++++++---------------------
1 file changed, 25 insertions(+), 31 deletions(-)

diff --git a/arch/arm64/kvm/va_layout.c b/arch/arm64/kvm/va_layout.c
index dab1fea4752a..a4f48c1ac28c 100644
--- a/arch/arm64/kvm/va_layout.c
+++ b/arch/arm64/kvm/va_layout.c
@@ -13,52 +13,46 @@
#include <asm/kvm_mmu.h>

/*
- * The LSB of the random hyp VA tag or 0 if no randomization is used.
+ * The LSB of the HYP VA tag
*/
static u8 tag_lsb;
/*
- * The random hyp VA tag value with the region bit if hyp randomization is used
+ * The HYP VA tag value with the region bit
*/
static u64 tag_val;
static u64 va_mask;

+/*
+ * We want to generate a hyp VA with the following format (with V ==
+ * vabits_actual):
+ *
+ * 63 ... V | V-1 | V-2 .. tag_lsb | tag_lsb - 1 .. 0
+ * ---------------------------------------------------------
+ * | 0000000 | hyp_va_msb | random tag | kern linear VA |
+ * |--------- tag_val -----------|----- va_mask ---|
+ *
+ * which does not conflict with the idmap regions.
+ */
__init void kvm_compute_layout(void)
{
phys_addr_t idmap_addr = __pa_symbol(__hyp_idmap_text_start);
u64 hyp_va_msb;
- int kva_msb;

/* Where is my RAM region? */
hyp_va_msb = idmap_addr & BIT(vabits_actual - 1);
hyp_va_msb ^= BIT(vabits_actual - 1);

- kva_msb = fls64((u64)phys_to_virt(memblock_start_of_DRAM()) ^
+ tag_lsb = fls64((u64)phys_to_virt(memblock_start_of_DRAM()) ^
(u64)(high_memory - 1));

- if (kva_msb == (vabits_actual - 1)) {
- /*
- * No space in the address, let's compute the mask so
- * that it covers (vabits_actual - 1) bits, and the region
- * bit. The tag stays set to zero.
- */
- va_mask = BIT(vabits_actual - 1) - 1;
- va_mask |= hyp_va_msb;
- } else {
- /*
- * We do have some free bits to insert a random tag.
- * Hyp VAs are now created from kernel linear map VAs
- * using the following formula (with V == vabits_actual):
- *
- * 63 ... V | V-1 | V-2 .. tag_lsb | tag_lsb - 1 .. 0
- * ---------------------------------------------------------
- * | 0000000 | hyp_va_msb | random tag | kern linear VA |
- */
- tag_lsb = kva_msb;
- va_mask = GENMASK_ULL(tag_lsb - 1, 0);
- tag_val = get_random_long() & GENMASK_ULL(vabits_actual - 2, tag_lsb);
- tag_val |= hyp_va_msb;
- tag_val >>= tag_lsb;
+ va_mask = GENMASK_ULL(tag_lsb - 1, 0);
+ tag_val = hyp_va_msb;
+
+ if (tag_lsb != (vabits_actual - 1)) {
+ /* We have some free bits to insert a random tag. */
+ tag_val |= get_random_long() & GENMASK_ULL(vabits_actual - 2, tag_lsb);
}
+ tag_val >>= tag_lsb;
}

static u32 compute_instruction(int n, u32 rd, u32 rn)
@@ -117,11 +111,11 @@ void __init kvm_update_va_mask(struct alt_instr *alt,
* VHE doesn't need any address translation, let's NOP
* everything.
*
- * Alternatively, if we don't have any spare bits in
- * the address, NOP everything after masking that
- * kernel VA.
+ * Alternatively, if the tag is zero (because the layout
+ * dictates it and we don't have any spare bits in the
+ * address), NOP everything after masking the kernel VA.
*/
- if (has_vhe() || (!tag_lsb && i > 0)) {
+ if (has_vhe() || (!tag_val && i > 0)) {
updptr[i] = cpu_to_le32(aarch64_insn_gen_nop());
continue;
}
--
2.20.1