Commit b220244d authored by James Morse's avatar James Morse Committed by Marc Zyngier

arm64: vgic-v2: Fix proxying of cpuif access

Proxying the cpuif accesses at EL2 makes use of vcpu_data_guest_to_host
and co, which check the endianness, which call into vcpu_read_sys_reg...
which isn't mapped at EL2 (it was inlined before, and got moved OoL
with the VHE optimizations).

The result is of course a nice panic. Let's add some specialized
cruft to keep the broken platforms that require this hack alive.

But, this code used vcpu_data_guest_to_host(), which expected us to
write the value to host memory, instead we have trapped the guest's
read or write to an mmio-device, and are about to replay it using the
host's readl()/writel() which also perform swabbing based on the host
endianness. This goes wrong when both host and guest are big-endian,
as readl()/writel() will undo the guest's swabbing, causing the
big-endian value to be written to device-memory.

What needs doing?
A big-endian guest will have pre-swabbed data before storing, undo this.
If its necessary for the host, writel() will re-swab it.

For a read a big-endian guest expects to swab the data after the load.
The hosts's readl() will correct for host endianness, giving us the
device-memory's value in the register. For a big-endian guest, swab it
as if we'd only done the load.

For a little-endian guest, nothing needs doing as readl()/writel() leave
the correct device-memory value in registers.

Tested on Juno with that rarest of things: a big-endian 64K host.
Based on a patch from Marc Zyngier.
Reported-by: default avatarSuzuki K Poulose <>
Fixes: bf8feb39 ("arm64: KVM: vgic-v2: Add GICV access from HYP")
Signed-off-by: default avatarJames Morse <>
Signed-off-by: default avatarMarc Zyngier <>
parent c3616a07
......@@ -18,11 +18,20 @@
#include <linux/compiler.h>
#include <linux/irqchip/arm-gic.h>
#include <linux/kvm_host.h>
#include <linux/swab.h>
#include <asm/kvm_emulate.h>
#include <asm/kvm_hyp.h>
#include <asm/kvm_mmu.h>
static bool __hyp_text __is_be(struct kvm_vcpu *vcpu)
if (vcpu_mode_is_32bit(vcpu))
return !!(read_sysreg_el2(spsr) & COMPAT_PSR_E_BIT);
return !!(read_sysreg(SCTLR_EL1) & SCTLR_ELx_EE);
* __vgic_v2_perform_cpuif_access -- perform a GICV access on behalf of the
* guest.
......@@ -64,14 +73,19 @@ int __hyp_text __vgic_v2_perform_cpuif_access(struct kvm_vcpu *vcpu)
addr += fault_ipa - vgic->vgic_cpu_base;
if (kvm_vcpu_dabt_iswrite(vcpu)) {
u32 data = vcpu_data_guest_to_host(vcpu,
vcpu_get_reg(vcpu, rd),
u32 data = vcpu_get_reg(vcpu, rd);
if (__is_be(vcpu)) {
/* guest pre-swabbed data, undo this for writel() */
data = swab32(data);
writel_relaxed(data, addr);
} else {
u32 data = readl_relaxed(addr);
vcpu_set_reg(vcpu, rd, vcpu_data_host_to_guest(vcpu, data,
if (__is_be(vcpu)) {
/* guest expects swabbed data */
data = swab32(data);
vcpu_set_reg(vcpu, rd, data);
return 1;
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