[PATCH v3 24/55] KVM: arm/arm64: vgic-new: Add ENABLE registers handlers

[christoffer.dall@linaro.org (Christoffer Dall)]

On Wed, May 11, 2016 at 02:04:13PM +0100, Andre Przywara wrote:
> Hi,
> 
> On 11/05/16 13:34, Christoffer Dall wrote:
> > On Fri, May 06, 2016 at 11:45:37AM +0100, Andre Przywara wrote:
> >> As the enable register handlers are shared between the v2 and v3
> >> emulation, their implementation goes into vgic-mmio.c, to be easily
> >> referenced from the v3 emulation as well later.
> >>
> >> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> >> ---
> >> Changelog RFC..v1:
> >> - use lower bits of address to determine IRQ number
> >> - remove TODO, confirmed to be fine
> >>
> >> Changelog v1 .. v2:
> >> - adapt to new MMIO framework
> >>
> >>  virt/kvm/arm/vgic/vgic-mmio-v2.c |  4 +--
> >>  virt/kvm/arm/vgic/vgic-mmio.c    | 56 ++++++++++++++++++++++++++++++++++++++++
> >>  virt/kvm/arm/vgic/vgic-mmio.h    | 11 ++++++++
> >>  3 files changed, 69 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/virt/kvm/arm/vgic/vgic-mmio-v2.c b/virt/kvm/arm/vgic/vgic-mmio-v2.c
> >> index 69e96f7..448d1da 100644
> >> --- a/virt/kvm/arm/vgic/vgic-mmio-v2.c
> >> +++ b/virt/kvm/arm/vgic/vgic-mmio-v2.c
> >> @@ -72,9 +72,9 @@ static const struct vgic_register_region vgic_v2_dist_registers[] = {
> >>  	REGISTER_DESC_WITH_BITS_PER_IRQ(GIC_DIST_IGROUP,
> >>  		vgic_mmio_read_rao, vgic_mmio_write_wi, 1),
> >>  	REGISTER_DESC_WITH_BITS_PER_IRQ(GIC_DIST_ENABLE_SET,
> >> -		vgic_mmio_read_raz, vgic_mmio_write_wi, 1),
> >> +		vgic_mmio_read_enable, vgic_mmio_write_senable, 1),
> >>  	REGISTER_DESC_WITH_BITS_PER_IRQ(GIC_DIST_ENABLE_CLEAR,
> >> -		vgic_mmio_read_raz, vgic_mmio_write_wi, 1),
> >> +		vgic_mmio_read_enable, vgic_mmio_write_cenable, 1),
> >>  	REGISTER_DESC_WITH_BITS_PER_IRQ(GIC_DIST_PENDING_SET,
> >>  		vgic_mmio_read_raz, vgic_mmio_write_wi, 1),
> >>  	REGISTER_DESC_WITH_BITS_PER_IRQ(GIC_DIST_PENDING_CLEAR,
> >> diff --git a/virt/kvm/arm/vgic/vgic-mmio.c b/virt/kvm/arm/vgic/vgic-mmio.c
> >> index 41cf4f4..077ae86 100644
> >> --- a/virt/kvm/arm/vgic/vgic-mmio.c
> >> +++ b/virt/kvm/arm/vgic/vgic-mmio.c
> >> @@ -46,6 +46,62 @@ void vgic_mmio_write_wi(struct kvm_vcpu *vcpu, gpa_t addr,
> >>  	/* Ignore */
> >>  }
> >>  
> >> +/*
> >> + * Read accesses to both GICD_ICENABLER and GICD_ISENABLER return the value
> >> + * of the enabled bit, so there is only one function for both here.
> >> + */
> >> +unsigned long vgic_mmio_read_enable(struct kvm_vcpu *vcpu,
> >> +				    gpa_t addr, unsigned int len)
> >> +{
> >> +	u32 intid = (addr & 0x7f) * 8;
> > 
> > is there anything we can do about this to make it more intuitive?  A
> > macro to generate the mask/offset based on bits per interrupt or
> > something?
> 
> Yes, something where you give it the address and the bits-per-IRQ and it
> tells you the IRQ number.
> Not sure it is advisable to squash this into v4 still?
> 
> > 
> >> +	u32 value = 0;
> >> +	int i;
> >> +
> >> +	/* Loop over all IRQs affected by this read */
> >> +	for (i = 0; i < len * 8; i++) {
> >> +		struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, vcpu, intid + i);
> >> +
> >> +		if (irq->enabled)
> >> +			value |= (1U << i);
> > 
> > I couldn't find the code anywhere that enforces word-aligned accesses to
> > these registers.  Do we have that?
> 
> Not that I am aware of. I was suggesting this since we have one in the
> IROUTER function. Architecturally we don't need to support halfword
> accesses, it's: byte + word, word only or double-word + word, depending
> on the actual register, IIRC.
> As a fix we can at least deny (read: ignore) halfword accesses in
> general in the dispatcher. Shall I do this (two two-liners)?
> I think byte and word accesses are safe with the existing handlers last
> time I checked.
> 
> > If that's not the case, doesn't this break of you do a non-word aligned
> > access?
> 
> Why would it? vgic_data_host_to_mmio_bus and extract_bytes should cover
> this, shouldn't they?
> 

I think this breaks on a simple byte access.  Let's say you are
accessing byte 1 (addr & 0x7ff == 1), then because you start your loop
at 0, you're going to set bits [7:0] in the value variable, and then
extract bits [15:8] in extract_bytes(), right?

-Christoffer