On 10.09.19 18:11, Julien Grall wrote:
Hi Oleksandr,

Hi, Julien



On 8/23/19 8:34 PM, Oleksandr Tyshchenko wrote:
From: Oleksandr Tyshchenko <oleksandr_tyshche...@epam.com>

There is a strict requirement for the IOMMU which wants to share
the P2M table with the CPU. The IOMMU's Stage-2 input size must be equal
to the P2M IPA size. It is not a problem when the IOMMU can support
all values the CPU supports. In that case, the IOMMU driver would just
use any "p2m_ipa_bits" value as is. But, there are cases when not.

In order to make P2M sharing possible on the platforms which
IPMMUs have a limitation in maximum Stage-2 input size introduce
the following logic.

First initialize the IOMMU subsystem and gather requirements regarding
the maximum IPA bits supported by each IOMMU device to figure out
the minimum value among them. In the P2M code, take into the account
the IOMMU requirements and choose suitable "pa_range" according
to the restricted "p2m_ipa_bits".

As I pointed in the previous version, all the code you modify is arm64 specific. For arm32, the number of IPA bits is hardcoded. So if you modify p2m_ipa_bits, you would end up to misconfigure VTCR. In other words, for Arm32, you need to check p2m_ipa_bits is at least 40-bits before overriding it.

But, all modifications with p2m_ipa_bits are done before setup_virt_paging(), where, actually, the p2m_ipa_bits is hard-coded to 40 bits. How can we end up misconfiguring VTCR for ARM32? Or I really missed something?





Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshche...@epam.com>
CC: Julien Grall <julien.gr...@arm.com>

---
Still RFC:

1. Patch assumes that IPMMU support is already in.
2. Not checked for the SMMU.

Changes since RFC V1 [1]:
    - Don't update p2m_ipa_bits by the IOMMU drivers directly,
      introduce p2m_restrict_ipa_bits()
    - Clarify patch subject/description
    - Add more comments to code
    - Check for equivalent "pabits" in setup_virt_paging()
    - Remove ASSERTs from the SMMU and IPMMU drivers

[1] https://lists.xenproject.org/archives/html/xen-devel/2019-08/msg02078.html
---
  xen/arch/arm/p2m.c                       | 33 ++++++++++++++++++++++++++++++--
  xen/arch/arm/setup.c                     | 11 +++++++++--
  xen/drivers/passthrough/arm/ipmmu-vmsa.c | 19 ++++--------------
  xen/drivers/passthrough/arm/smmu.c       | 16 ++++++++--------
  xen/include/asm-arm/p2m.h                |  8 ++++++++
  5 files changed, 60 insertions(+), 27 deletions(-)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 2374e92..f742d9c 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -34,7 +34,8 @@ static unsigned int __read_mostly max_vmid = MAX_VMID_8_BIT;
    #define P2M_ROOT_PAGES    (1<<P2M_ROOT_ORDER)
  -unsigned int __read_mostly p2m_ipa_bits;
+/* Larger than any possible value */

I think it would be worth explaining that this is required so the number of P2M bits can be restricted by external entity (e.g IOMMU).

ok, will add explanation




+unsigned int __read_mostly p2m_ipa_bits = 64;
    /* Helpers to lookup the properties of each level */
  static const paddr_t level_masks[] =
@@ -1912,6 +1913,16 @@ struct page_info *get_page_from_gva(struct vcpu *v, vaddr_t va,
      return page;
  }
  +void __init p2m_restrict_ipa_bits(unsigned int iommu_ipa_bits)

The name of the function is quite generic as most of the code in it. So can we avoid use the term IOMMU in it?

yes, will do




+{
+    /*
+     * Calculate the minimum of the maximum IPA bits that any IOMMU
+     * can support.
+     */
+    if ( iommu_ipa_bits < p2m_ipa_bits )
+        p2m_ipa_bits = iommu_ipa_bits;
+}
+
  /* VTCR value to be configured by all CPUs. Set only once by the boot CPU */
  static uint32_t __read_mostly vtcr;
  @@ -1966,10 +1977,28 @@ void __init setup_virt_paging(void)
          [7] = { 0 }  /* Invalid */
      };
  -    unsigned int cpu;
+    unsigned int i, cpu;
      unsigned int pa_range = 0x10; /* Larger than any possible value */
      bool vmid_8_bit = false;
  +    if ( iommu_enabled )

Could we make this IOMMU-agnostic? The main reason to convert from p2m_ipa_bits to pa_range is to cater the rest of the code.

But we could rework the code to do the computation with p2m_ipa_bits and then look-up for the pa_range.

I am afraid, I don't completely understand your idea of making this IOMMU-agnostic and what I should do...


+    {
+        /*
+         * Choose suitable "pa_range" according to the IOMMU requirements
+         * (restricted "p2m_ipa_bits" value).
+         * As P2M table is always configured with IPA bits == PA bits,
+         * check for equivalent "pabits" and store it's index.
+         */
+        for ( i = 0; i < ARRAY_SIZE(pa_range_info); i++ )
+        {
+            if ( p2m_ipa_bits == pa_range_info[i].pabits )
+            {
+                pa_range = i;
+                break;
+            }
+        }
+    }
+
      for_each_online_cpu ( cpu )
      {
          const struct cpuinfo_arm *info = &cpu_data[cpu];
diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index 51a6677..413f3e6 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -936,12 +936,19 @@ void __init start_xen(unsigned long boot_phys_offset,
      printk("Brought up %ld CPUs\n", (long)num_online_cpus());
      /* TODO: smp_cpus_done(); */
  -    setup_virt_paging();
-
+    /*
+     * The IOMMU subsystem must be initialized before P2M as we need to gather +     * requirements regarding the maximum IPA bits supported by each IOMMU +     * device to figure out the minimum value among them. The P2M code will +     * choose suitable "pa_range" according to the restricted "p2m_ipa_bits"
+     * value.
+     */

This is a bit too verbose, implementation details are not necessary here and increasing the risk to have bit rot comment. So how about:

"The IOMMU subsystem must be initialized before the P2M as we need to gather requirements regarding the maximum IPA bit supported by each IOMMU."?

you are right, will update a comment




      rc = iommu_setup();
      if ( !iommu_enabled && rc != -ENODEV )
          panic("Couldn't configure correctly all the IOMMUs.");
  +    setup_virt_paging();
+
      do_initcalls();
        /*
diff --git a/xen/drivers/passthrough/arm/ipmmu-vmsa.c b/xen/drivers/passthrough/arm/ipmmu-vmsa.c
index ec543c3..d2e36a4 100644
--- a/xen/drivers/passthrough/arm/ipmmu-vmsa.c
+++ b/xen/drivers/passthrough/arm/ipmmu-vmsa.c
@@ -1314,23 +1314,12 @@ static __init int ipmmu_init(struct dt_device_node *node, const void *data)
          return -ENODEV;
      }
      else
-    {
          /*
-         * As 4-level translation table is not supported in IPMMU, we need -         * to check IPA size used for P2M table beforehand to be sure it is
-         * 3-level and the IPMMU will be able to use it.
-         *
-         * TODO: First initialize the IOMMU and gather the requirements and -         * then initialize the P2M. In the P2M code, take into the account
-         * the IOMMU requirements and restrict "pa_range" if necessary.
+         * Set maximum Stage-2 input size supported by the IPMMU. We expect +         * the P2M code will take into the account the IOMMU requirements and
+         * choose suitable "pa_range".

I would drop the last sentence.

ok. will do




           */
-        if ( IPMMU_MAX_P2M_IPA_BITS < p2m_ipa_bits )
-        {
-            printk_once(XENLOG_ERR "ipmmu: P2M IPA size is not supported (P2M=%u IPMMU=%u)!\n",
-                        p2m_ipa_bits, IPMMU_MAX_P2M_IPA_BITS);
-            return -ENODEV;
-        }
-    }
+        p2m_restrict_ipa_bits(IPMMU_MAX_P2M_IPA_BITS);
        ret = ipmmu_probe(node);
      if ( ret )
diff --git a/xen/drivers/passthrough/arm/smmu.c b/xen/drivers/passthrough/arm/smmu.c
index 8ae986a..2b10c6e 100644
--- a/xen/drivers/passthrough/arm/smmu.c
+++ b/xen/drivers/passthrough/arm/smmu.c
@@ -2198,14 +2198,14 @@ static int arm_smmu_device_cfg_probe(struct arm_smmu_device *smmu)       size = arm_smmu_id_size_to_bits((id >> ID2_IAS_SHIFT) & ID2_IAS_MASK);       smmu->s1_output_size = min_t(unsigned long, PHYS_MASK_SHIFT, size);
  -    /* Xen: Stage-2 input size has to match p2m_ipa_bits.  */
-    if (size < p2m_ipa_bits) {
-        dev_err(smmu->dev,
-            "P2M IPA size not supported (P2M=%u SMMU=%lu)!\n",
-            p2m_ipa_bits, size);
-        return -ENODEV;
-    }
-    smmu->s2_input_size = p2m_ipa_bits;
+    /*
+     * Xen:
+     * Set maximum Stage-2 input size supported by the SMMU. We expect
+     * the P2M code will take into the account the IOMMU requirements and
+     * choose suitable "pa_range".

Same here.

ok


--
Regards,

Oleksandr Tyshchenko


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