Hi Marc,
On 4/1/21 3:42 PM, Marc Zyngier wrote:
> Hi Eric,
>
> On Thu, 01 Apr 2021 09:52:37 +0100,
> Eric Auger <eric.auger@xxxxxxxxxx> wrote:
>>
>> Commit 23bde34771f1 ("KVM: arm64: vgic-v3: Drop the
>> reporting of GICR_TYPER.Last for userspace") temporarily fixed
>> a bug identified when attempting to access the GICR_TYPER
>> register before the redistributor region setting, but dropped
>> the support of the LAST bit.
>>
>> Emulating the GICR_TYPER.Last bit still makes sense for
>> architecture compliance though. This patch restores its support
>> (if the redistributor region was set) while keeping the code safe.
>>
>> We introduce a new helper, vgic_mmio_vcpu_rdist_is_last() which
>> computes whether a redistributor is the highest one of a series
>> of redistributor contributor pages.
>>
>> The spec says "Indicates whether this Redistributor is the
>> highest-numbered Redistributor in a series of contiguous
>> Redistributor pages."
>>
>> The code is a bit convulated since there is no guarantee
>
> nit: convoluted
>
>> redistributors are added in a given reditributor region in
>> ascending order. In that case the current implementation was
>> wrong. Also redistributor regions can be contiguous
>> and registered in non increasing base address order.
>>
>> So the index of redistributors are stored in an array within
>> the redistributor region structure.
>>
>> With this new implementation we do not need to have a uaccess
>> read accessor anymore.
>>
>> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
>
> This patch also hurt my head, a lot more than the first one. See
> below.
>
>> ---
>> arch/arm64/kvm/vgic/vgic-init.c | 7 +--
>> arch/arm64/kvm/vgic/vgic-mmio-v3.c | 97 ++++++++++++++++++++----------
>> arch/arm64/kvm/vgic/vgic.h | 1 +
>> include/kvm/arm_vgic.h | 3 +
>> 4 files changed, 73 insertions(+), 35 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
>> index cf6faa0aeddb2..61150c34c268c 100644
>> --- a/arch/arm64/kvm/vgic/vgic-init.c
>> +++ b/arch/arm64/kvm/vgic/vgic-init.c
>> @@ -190,6 +190,7 @@ int kvm_vgic_vcpu_init(struct kvm_vcpu *vcpu)
>> int i;
>>
>> vgic_cpu->rd_iodev.base_addr = VGIC_ADDR_UNDEF;
>> + vgic_cpu->index = vcpu->vcpu_id;
>
> Is it so that vgic_cpu->index is always equal to vcpu_id? If so, why
> do we need another field? We can always get to the vcpu using a
> container_of().
>
>>
>> INIT_LIST_HEAD(&vgic_cpu->ap_list_head);
>> raw_spin_lock_init(&vgic_cpu->ap_list_lock);
>> @@ -338,10 +339,8 @@ static void kvm_vgic_dist_destroy(struct kvm *kvm)
>> dist->vgic_dist_base = VGIC_ADDR_UNDEF;
>>
>> if (dist->vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3) {
>> - list_for_each_entry_safe(rdreg, next, &dist->rd_regions, list) {
>> - list_del(&rdreg->list);
>> - kfree(rdreg);
>> - }
>> + list_for_each_entry_safe(rdreg, next, &dist->rd_regions, list)
>> + vgic_v3_free_redist_region(rdreg);
>
> Consider moving the introduction of vgic_v3_free_redist_region() into
> a separate patch. On its own, that's a good readability improvement.
>
>> INIT_LIST_HEAD(&dist->rd_regions);
>> } else {
>> dist->vgic_cpu_base = VGIC_ADDR_UNDEF;
>> diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
>> index 987e366c80008..f6a7eed1d6adb 100644
>> --- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c
>> +++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
>> @@ -251,45 +251,57 @@ static void vgic_mmio_write_v3r_ctlr(struct kvm_vcpu *vcpu,
>> vgic_enable_lpis(vcpu);
>> }
>>
>> +static bool vgic_mmio_vcpu_rdist_is_last(struct kvm_vcpu *vcpu)
>> +{
>> + struct vgic_dist *vgic = &vcpu->kvm->arch.vgic;
>> + struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
>> + struct vgic_redist_region *rdreg = vgic_cpu->rdreg;
>> +
>> + if (!rdreg)
>> + return false;
>> +
>> + if (rdreg->count && vgic_cpu->rdreg_index == (rdreg->count - 1)) {
>> + /* check whether there is no other contiguous rdist region */
>> + struct list_head *rd_regions = &vgic->rd_regions;
>> + struct vgic_redist_region *iter;
>> +
>> + list_for_each_entry(iter, rd_regions, list) {
>> + if (iter->base == rdreg->base + rdreg->count * KVM_VGIC_V3_REDIST_SIZE &&
>> + iter->free_index > 0) {
>> + /* check the first rdist index of this region, if any */
>> + if (vgic_cpu->index < iter->rdist_indices[0])
>> + return false;
>
> rdist_indices[] contains the vcpu_id of the vcpu associated with a
> given RD in the region. At this stage, you have established that there
> is another region that is contiguous with the one associated with our
> vcpu. You also know that this adjacent region has a vcpu mapped in
> (free_index isn't 0). Isn't that enough to declare that our vcpu isn't
> last? I definitely don't understand what the index comparison does
> here.
Assume the following case:
2 RDIST region
region #0 contains rdist 1, 2, 4
region #1, adjacent to #0 contains rdist 3
Spec days:
"Indicates whether this Redistributor is the
highest-numbered Redistributor in a series of contiguous
Redistributor pages."
To me 4 is last and 3 is last too.
>
> It also seem to me that some of the complexity could be eliminated if
> the regions were kept ordered at list insertion time.
yes
>
>> + }
>> + }
>> + } else if (vgic_cpu->rdreg_index < rdreg->free_index - 1) {
>> + /* look at the index of next rdist */
>> + int next_rdist_index = rdreg->rdist_indices[vgic_cpu->rdreg_index + 1];
>> +
>> + if (vgic_cpu->index < next_rdist_index)
>> + return false;
>
> Same thing here. We are in the middle of the allocated part of a
> region, which means we cannot be last. I still don't get the index
> check.
Because within a region, nothing hinders rdist from being allocated in
non ascending order. I exercise those cases in the kvmselftests
one single RDIST region with the following rdists allocated there:
1, 3, 2
3 and 2 are "last", right? Or did I miss something. Yes that's totally
not natural to do that kind of allocation but the API allows to do that.
>
>> + }
>> + return true;
>> +}
>> +
>> static unsigned long vgic_mmio_read_v3r_typer(struct kvm_vcpu *vcpu,
>> gpa_t addr, unsigned int len)
>> {
>> unsigned long mpidr = kvm_vcpu_get_mpidr_aff(vcpu);
>> - struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
>> - struct vgic_redist_region *rdreg = vgic_cpu->rdreg;
>> int target_vcpu_id = vcpu->vcpu_id;
>> - gpa_t last_rdist_typer = rdreg->base + GICR_TYPER +
>> - (rdreg->free_index - 1) * KVM_VGIC_V3_REDIST_SIZE;
>> u64 value;
>>
>> value = (u64)(mpidr & GENMASK(23, 0)) << 32;
>> value |= ((target_vcpu_id & 0xffff) << 8);
>>
>> - if (addr == last_rdist_typer)
>> + if (vgic_has_its(vcpu->kvm))
>> + value |= GICR_TYPER_PLPIS;
>> +
>> + if (vgic_mmio_vcpu_rdist_is_last(vcpu))
>> value |= GICR_TYPER_LAST;
>> - if (vgic_has_its(vcpu->kvm))
>> - value |= GICR_TYPER_PLPIS;
>>
>> return extract_bytes(value, addr & 7, len);
>> }
>>
>> -static unsigned long vgic_uaccess_read_v3r_typer(struct kvm_vcpu *vcpu,
>> - gpa_t addr, unsigned int len)
>> -{
>> - unsigned long mpidr = kvm_vcpu_get_mpidr_aff(vcpu);
>> - int target_vcpu_id = vcpu->vcpu_id;
>> - u64 value;
>> -
>> - value = (u64)(mpidr & GENMASK(23, 0)) << 32;
>> - value |= ((target_vcpu_id & 0xffff) << 8);
>> -
>> - if (vgic_has_its(vcpu->kvm))
>> - value |= GICR_TYPER_PLPIS;
>> -
>> - /* reporting of the Last bit is not supported for userspace */
>> - return extract_bytes(value, addr & 7, len);
>> -}
>> -
>> static unsigned long vgic_mmio_read_v3r_iidr(struct kvm_vcpu *vcpu,
>> gpa_t addr, unsigned int len)
>> {
>> @@ -612,7 +624,7 @@ static const struct vgic_register_region vgic_v3_rd_registers[] = {
>> VGIC_ACCESS_32bit),
>> REGISTER_DESC_WITH_LENGTH_UACCESS(GICR_TYPER,
>> vgic_mmio_read_v3r_typer, vgic_mmio_write_wi,
>> - vgic_uaccess_read_v3r_typer, vgic_mmio_uaccess_write_wi, 8,
>> + NULL, vgic_mmio_uaccess_write_wi, 8,
>> VGIC_ACCESS_64bit | VGIC_ACCESS_32bit),
>> REGISTER_DESC_WITH_LENGTH(GICR_WAKER,
>> vgic_mmio_read_raz, vgic_mmio_write_wi, 4,
>> @@ -714,6 +726,16 @@ int vgic_register_redist_iodev(struct kvm_vcpu *vcpu)
>> return -EINVAL;
>>
>> vgic_cpu->rdreg = rdreg;
>> + vgic_cpu->rdreg_index = rdreg->free_index;
>> + if (!rdreg->count) {
>> + void *p = krealloc(rdreg->rdist_indices,
>> + (vgic_cpu->rdreg_index + 1) * sizeof(u32),
>> + GFP_KERNEL);
>> + if (!p)
>> + return -ENOMEM;
>> + rdreg->rdist_indices = p;
>> + }
>> + rdreg->rdist_indices[vgic_cpu->rdreg_index] = vgic_cpu->index;
>
> I think I really have a problem with this array, which comes from me
> not understanding the two checks I previously commented on.
I hope the above clarified the array need.
>
> If we stick to the definition of 'Last', all that matters is the
> position of the RD in a region (rdreg_index) and potentially the
> presence of another contiguous region with allocated RDs in it.
>
> IIUC, the checks should read like this:
>
> if (vcpu->rdreg_index < (vcpu->rdreg->free_index - 1))
> last = false;
> else if (vcpu->rdreg_index == (vcpu->rdreg->free_index - 1) &&
> adjacent_region(vcpu->rdreg)->free_index > 0)
> last = false;
> else
> last = true;
>
> So why do we need to track the vcpu_id associated to a region?
because the redistributors within a region can be in random order.
That's why I need to store their number.
Does that make more sense?
Thanks
Eric
>
>>
>> rd_base = rdreg->base + rdreg->free_index * KVM_VGIC_V3_REDIST_SIZE;
>>
>> @@ -768,7 +790,7 @@ static int vgic_register_all_redist_iodevs(struct kvm *kvm)
>> }
>>
>> /**
>> - * vgic_v3_insert_redist_region - Insert a new redistributor region
>> + * vgic_v3_alloc_redist_region - Allocate a new redistributor region
>> *
>> * Performs various checks before inserting the rdist region in the list.
>> * Those tests depend on whether the size of the rdist region is known
>> @@ -782,8 +804,8 @@ static int vgic_register_all_redist_iodevs(struct kvm *kvm)
>> *
>> * Return 0 on success, < 0 otherwise
>> */
>> -static int vgic_v3_insert_redist_region(struct kvm *kvm, uint32_t index,
>> - gpa_t base, uint32_t count)
>> +static int vgic_v3_alloc_redist_region(struct kvm *kvm, uint32_t index,
>> + gpa_t base, uint32_t count)
>> {
>> struct vgic_dist *d = &kvm->arch.vgic;
>> struct vgic_redist_region *rdreg;
>> @@ -839,6 +861,13 @@ static int vgic_v3_insert_redist_region(struct kvm *kvm, uint32_t index,
>> rdreg->count = count;
>> rdreg->free_index = 0;
>> rdreg->index = index;
>> + if (count) {
>> + rdreg->rdist_indices = kcalloc(count, sizeof(u32), GFP_KERNEL);
>> + if (!rdreg->rdist_indices) {
>> + ret = -ENOMEM;
>> + goto free;
>> + }
>> + }
>>
>> list_add_tail(&rdreg->list, rd_regions);
>> return 0;
>> @@ -847,11 +876,18 @@ static int vgic_v3_insert_redist_region(struct kvm *kvm, uint32_t index,
>> return ret;
>> }
>>
>> +void vgic_v3_free_redist_region(struct vgic_redist_region *rdreg)
>> +{
>> + list_del(&rdreg->list);
>> + kfree(rdreg->rdist_indices);
>> + kfree(rdreg);
>> +}
>> +
>> int vgic_v3_set_redist_base(struct kvm *kvm, u32 index, u64 addr, u32 count)
>> {
>> int ret;
>>
>> - ret = vgic_v3_insert_redist_region(kvm, index, addr, count);
>> + ret = vgic_v3_alloc_redist_region(kvm, index, addr, count);
>> if (ret)
>> return ret;
>>
>> @@ -864,8 +900,7 @@ int vgic_v3_set_redist_base(struct kvm *kvm, u32 index, u64 addr, u32 count)
>> struct vgic_redist_region *rdreg;
>>
>> rdreg = vgic_v3_rdist_region_from_index(kvm, index);
>> - list_del(&rdreg->list);
>> - kfree(rdreg);
>> + vgic_v3_free_redist_region(rdreg);
>> return ret;
>> }
>>
>> diff --git a/arch/arm64/kvm/vgic/vgic.h b/arch/arm64/kvm/vgic/vgic.h
>> index 64fcd75111108..bc418c2c12141 100644
>> --- a/arch/arm64/kvm/vgic/vgic.h
>> +++ b/arch/arm64/kvm/vgic/vgic.h
>> @@ -293,6 +293,7 @@ vgic_v3_rd_region_size(struct kvm *kvm, struct vgic_redist_region *rdreg)
>>
>> struct vgic_redist_region *vgic_v3_rdist_region_from_index(struct kvm *kvm,
>> u32 index);
>> +void vgic_v3_free_redist_region(struct vgic_redist_region *rdreg);
>>
>> bool vgic_v3_rdist_overlap(struct kvm *kvm, gpa_t base, size_t size);
>>
>> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
>> index 3d74f1060bd18..9a3f060ac3547 100644
>> --- a/include/kvm/arm_vgic.h
>> +++ b/include/kvm/arm_vgic.h
>> @@ -197,6 +197,7 @@ struct vgic_redist_region {
>> gpa_t base;
>> u32 count; /* number of redistributors or 0 if single region */
>> u32 free_index; /* index of the next free redistributor */
>> + int *rdist_indices; /* indices of the redistributors */
>
> You are treating it as an array of u32 when allocating it. Please
> choose one type or the other.
>
>> struct list_head list;
>> };
>>
>> @@ -322,6 +323,8 @@ struct vgic_cpu {
>> */
>> struct vgic_io_device rd_iodev;
>> struct vgic_redist_region *rdreg;
>> + u32 rdreg_index;
>> + int index; /* vcpu index */
>>
>> /* Contains the attributes and gpa of the LPI pending tables. */
>> u64 pendbaser;
>
> Thanks,
>
> M.
>
_______________________________________________
kvmarm mailing list
kvmarm@xxxxxxxxxxxxxxxxxxxxx
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
