vmm: Implement translate_gva on AArch64

On AArch64, `translate_gva` API is not provided by KVM. We implemented
it in VMM by walking through translation tables.

Address translation is big topic, here we only focus the scenario that
happens in VMM while debugging kernel. This `translate_gva`
implementation is restricted to:
 - Exception Level 1
 - Translate high address range only (kernel space)

This implementation supports following Arm-v8a features related to
address translation:
 - FEAT_LPA
 - FEAT_LVA
 - FEAT_LPA2

The implementation supports page sizes of 4KiB, 16KiB and 64KiB.

Signed-off-by: Michael Zhao <michael.zhao@arm.com>

arch/src/aarch64/regs.rs

@@ -39,3 +39,6 @@ macro_rules! arm64_sys_reg {
 }
 
 arm64_sys_reg!(MPIDR_EL1, 3, 0, 0, 0, 5);
+arm64_sys_reg!(ID_AA64MMFR0_EL1, 3, 0, 0, 7, 0);
+arm64_sys_reg!(TTBR1_EL1, 3, 0, 2, 0, 1);
+arm64_sys_reg!(TCR_EL1, 3, 0, 2, 0, 2);

vmm/src/cpu.rs

@@ -29,6 +29,8 @@ use crate::GuestMemoryMmap;
 use crate::CPU_MANAGER_SNAPSHOT_ID;
 use acpi_tables::{aml, aml::Aml, sdt::Sdt};
 use anyhow::anyhow;
+#[cfg(all(target_arch = "aarch64", feature = "gdb"))]
+use arch::aarch64::regs;
 use arch::EntryPoint;
 use arch::NumaNodes;
 use devices::interrupt_controller::InterruptController;
@@ -78,6 +80,18 @@ use vm_migration::{
 use vmm_sys_util::eventfd::EventFd;
 use vmm_sys_util::signal::{register_signal_handler, SIGRTMIN};
 
+#[cfg(all(target_arch = "aarch64", feature = "gdb"))]
+/// Extract the specified bits of a 64-bit integer.
+/// For example, to extrace 2 bits from offset 1 (zero based) of `6u64`,
+/// following expression should return 3 (`0b11`):
+/// `extract_bits_64!(0b0000_0110u64, 1, 2)`
+///
+macro_rules! extract_bits_64 {
+    ($value: tt, $offset: tt, $length: tt) => {
+        ($value >> $offset) & (!0u64 >> (64 - $length))
+    };
+}
+
 pub const CPU_MANAGER_ACPI_SIZE: usize = 0xc;
 
 #[derive(Debug, Error)]
@@ -145,6 +159,10 @@ pub enum Error {
     #[error("Error translating virtual address: {0}")]
     TranslateVirtualAddress(#[source] hypervisor::HypervisorCpuError),
 
+    #[cfg(all(target_arch = "aarch64", feature = "gdb"))]
+    #[error("Error translating virtual address: {0}")]
+    TranslateVirtualAddress(#[source] anyhow::Error),
+
     #[cfg(all(feature = "amx", target_arch = "x86_64"))]
     #[error("Error setting up AMX: {0}")]
     AmxEnable(#[source] anyhow::Error),
@@ -1491,9 +1509,168 @@ impl CpuManager {
         Ok(gpa)
     }
 
+    ///
+    /// On AArch64, `translate_gva` API is not provided by KVM. We implemented
+    /// it in VMM by walking through translation tables.
+    ///
+    /// Address translation is big topic, here we only focus the scenario that
+    /// happens in VMM while debugging kernel. This `translate_gva`
+    /// implementation is restricted to:
+    /// - Exception Level 1
+    /// - Translate high address range only (kernel space)
+    ///
+    /// This implementation supports following Arm-v8a features related to
+    /// address translation:
+    /// - FEAT_LPA
+    /// - FEAT_LVA
+    /// - FEAT_LPA2
+    ///
     #[cfg(all(target_arch = "aarch64", feature = "gdb"))]
     fn translate_gva(&self, cpu_id: u8, gva: u64) -> Result<u64> {
-        unimplemented!()
+        let tcr_el1: u64 = self.vcpus[usize::from(cpu_id)]
+            .lock()
+            .unwrap()
+            .vcpu
+            .get_sys_reg(regs::TCR_EL1)
+            .map_err(|e| Error::TranslateVirtualAddress(e.into()))?;
+        let ttbr1_el1: u64 = self.vcpus[usize::from(cpu_id)]
+            .lock()
+            .unwrap()
+            .vcpu
+            .get_sys_reg(regs::TTBR1_EL1)
+            .map_err(|e| Error::TranslateVirtualAddress(e.into()))?;
+        let id_aa64mmfr0_el1: u64 = self.vcpus[usize::from(cpu_id)]
+            .lock()
+            .unwrap()
+            .vcpu
+            .get_sys_reg(regs::ID_AA64MMFR0_EL1)
+            .map_err(|e| Error::TranslateVirtualAddress(e.into()))?;
+
+        // Bit 55 of the VA determines the range, high (0xFFFxxx...)
+        // or low (0x000xxx...).
+        let high_range = extract_bits_64!(gva, 55, 1);
+        if high_range == 0 {
+            info!("VA (0x{:x}) range is not supported!", gva);
+            return Ok(gva);
+        }
+
+        // High range size offset
+        let tsz = extract_bits_64!(tcr_el1, 16, 6);
+        // Granule size
+        let tg = extract_bits_64!(tcr_el1, 30, 2);
+        // Indication of 48-bits (0) or 52-bits (1) for FEAT_LPA2
+        let ds = extract_bits_64!(tcr_el1, 59, 1);
+
+        if tsz == 0 {
+            info!("VA translation is not ready!");
+            return Ok(gva);
+        }
+
+        // VA size is determined by TCR_BL1.T1SZ
+        let va_size = 64 - tsz;
+        // Number of bits in VA consumed in each level of translation
+        let stride = match tg {
+            3 => 13, // 64KB granule size
+            1 => 11, // 16KB granule size
+            _ => 9,  // 4KB, default
+        };
+        // Starting level of walking
+        let mut level = 4 - (va_size - 4) / stride;
+
+        // PA or IPA size is determined
+        let tcr_ips = extract_bits_64!(tcr_el1, 32, 3);
+        #[allow(clippy::identity_op)]
+        let pa_range = extract_bits_64!(id_aa64mmfr0_el1, 0, 4);
+        // The IPA size in TCR_BL1 and PA Range in ID_AA64MMFR0_EL1 should match.
+        // To be safe, we use the minimum value if they are different.
+        let pa_range = std::cmp::min(tcr_ips, pa_range);
+        // PA size in bits
+        let pa_size = match pa_range {
+            0 => 32,
+            1 => 36,
+            2 => 40,
+            3 => 42,
+            4 => 44,
+            5 => 48,
+            6 => 52,
+            _ => {
+                return Err(Error::TranslateVirtualAddress(anyhow!(format!(
+                    "PA range not supported {}",
+                    pa_range
+                ))))
+            }
+        };
+
+        let indexmask_grainsize = (!0u64) >> (64 - (stride + 3));
+        let mut indexmask = (!0u64) >> (64 - (va_size - (stride * (4 - level))));
+        // If FEAT_LPA2 is present, the translation table descriptor holds
+        // 50 bits of the table address of next level.
+        // Otherwise, it is 48 bits.
+        let descaddrmask = if ds == 1 {
+            !0u64 >> (64 - 50) // mask with 50 least significant bits
+        } else {
+            !0u64 >> (64 - 48) // mask with 48 least significant bits
+        };
+        let descaddrmask = descaddrmask & !indexmask_grainsize;
+
+        // Translation table base address
+        #[allow(clippy::identity_op)]
+        let mut descaddr: u64 = extract_bits_64!(ttbr1_el1, 0, 48);
+        // In the case of FEAT_LPA and FEAT_LPA2, the initial translation table
+        // addresss bits [48:51] comes from TTBR1_EL1 bits [2:5].
+        if pa_size == 52 {
+            descaddr |= extract_bits_64!(ttbr1_el1, 2, 4) << 48;
+        }
+
+        // Loop through tables of each level
+        loop {
+            // Table offset for current level
+            let table_offset: u64 = (gva >> (stride * (4 - level))) & indexmask;
+            descaddr |= table_offset;
+            descaddr &= !7u64;
+
+            let mut buf = [0; 8];
+            self.vm_memory
+                .memory()
+                .read(&mut buf, GuestAddress(descaddr))
+                .map_err(|e| Error::TranslateVirtualAddress(e.into()))?;
+            let descriptor = u64::from_le_bytes(buf);
+
+            descaddr = descriptor & descaddrmask;
+            // In the case of FEAT_LPA, the next-level translation table address
+            // bits [48:51] comes from bits [12:15] of the current descriptor.
+            // For FEAT_LPA2, the next-level translation table address
+            // bits [50:51] comes from bits [8:9] of the current descriptor,
+            // bits [48:49] comes from bits [48:49] of the descriptor which was
+            // handled previously.
+            if pa_size == 52 {
+                if ds == 1 {
+                    // FEAT_LPA2
+                    descaddr |= extract_bits_64!(descriptor, 8, 2) << 50;
+                } else {
+                    // FEAT_LPA
+                    descaddr |= extract_bits_64!(descriptor, 12, 4) << 48;
+                }
+            }
+
+            if (descriptor & 2) != 0 && (level < 3) {
+                // This is a table entry. Go down to next level.
+                level += 1;
+                indexmask = indexmask_grainsize;
+                continue;
+            }
+
+            break;
+        }
+
+        // We have reached either:
+        // - a page entry at level 3 or
+        // - a block entry at level 1 or 2
+        let page_size = 1u64 << ((stride * (4 - level)) + 3);
+        descaddr &= !(page_size - 1);
+        descaddr |= gva & (page_size - 1);
+
+        Ok(descaddr)
     }
 }