From e81c51c49bcceb3cb7de3ef2c3ec3d819de3fbcd Mon Sep 17 00:00:00 2001
From: Oliver Anderson <oliver.anderson@cyberus-technology.de>
Date: Fri, 20 Mar 2026 17:47:23 +0100
Subject: [PATCH] arch: CpuidAdjustments type

Introduce a type for adjusting CPUID entries.

Signed-off-by: Oliver Anderson <oliver.anderson@cyberus-technology.de>
On-behalf-of: SAP oliver.anderson@sap.com
---
 .../x86_64/cpu_profile/cpuid_adjustments.rs   | 117 ++++++++++++++++++
 1 file changed, 117 insertions(+)

diff --git a/arch/src/x86_64/cpu_profile/cpuid_adjustments.rs b/arch/src/x86_64/cpu_profile/cpuid_adjustments.rs
index 10ae1bb61..ac3f58dfc 100644
--- a/arch/src/x86_64/cpu_profile/cpuid_adjustments.rs
+++ b/arch/src/x86_64/cpu_profile/cpuid_adjustments.rs
@@ -8,7 +8,10 @@
 
 use std::ops::RangeInclusive;
 
+use hypervisor::arch::x86::CpuIdEntry;
+use log::error;
 use serde::{Deserialize, Serialize};
+use thiserror::Error;
 
 use crate::x86_64::{CpuidReg, deserialize_u32_hex, serialize_u32_hex};
 
@@ -64,3 +67,117 @@ fn deserialize_range_hex<'de, D: serde::Deserializer<'de>>(
         ProvisionalRangeInclusive::deserialize(deserializer)?;
     Ok(start..=end)
 }
+
+/// Used for adjusting an entire cpuid output register (EAX, EBX, ECX or EDX).
+///
+/// Instances of this struct typically adjust CPUID according to the following
+/// formula: `cpuid_reg_value = (self.mask & cpuid_reg_value) | self.replacements`.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+pub struct CpuidOutputRegisterAdjustments {
+    /// Packs values to be placed into the given CPUID output register.
+    #[serde(
+        serialize_with = "serialize_u32_hex",
+        deserialize_with = "deserialize_u32_hex"
+    )]
+    pub replacements: u32,
+    /// Used to zero out the area `replacements` occupy. This mask is not necessarily !replacements, as replacements
+    /// may pack values of different types that occupy varying ranges of bits.
+    ///
+    /// Bit ranges within a CPUID output register that are **not** supposed to be replaced/overwritten should be set in
+    /// this mask.
+    #[serde(
+        serialize_with = "serialize_u32_hex",
+        deserialize_with = "deserialize_u32_hex"
+    )]
+    pub mask: u32,
+}
+
+/// Error type indicating that expected CPUID entries could not be found.
+///
+/// This type does not record which entries could not be found as we do not
+/// expect this to be actionable at runtime. Instead we encourage logging such
+/// violations when and where they are detected.
+#[derive(Debug, Error)]
+#[error("Required CPUID entries not found")]
+pub struct MissingCpuidEntriesError;
+
+impl CpuidOutputRegisterAdjustments {
+    /// Adjust the given `cpuid_output_register` by retaining and replacing values according to `self`.
+    fn adjust(self, cpuid_output_register: &mut u32) {
+        *cpuid_output_register &= self.mask;
+        *cpuid_output_register |= self.replacements;
+    }
+
+    /// Adjust `cpuid` according to the given `adjustments`.
+    ///
+    /// The returned vector of cpuid entries covers the same CPUID (sub-) leaves as the given `cpuid` input,
+    /// but values without matching [`CpuidParameters`] are zeroed out.
+    ///
+    /// # Errors
+    ///
+    /// An error is returned if an entry cannot be found for an adjustment describing non-zero replacements.
+    pub(super) fn adjust_cpuid_entries(
+        mut cpuid: Vec<CpuIdEntry>,
+        adjustments: &[(CpuidParameters, Self)],
+    ) -> Result<Vec<CpuIdEntry>, MissingCpuidEntriesError> {
+        for entry in &mut cpuid {
+            for (reg, reg_value) in [
+                (CpuidReg::EAX, &mut entry.eax),
+                (CpuidReg::EBX, &mut entry.ebx),
+                (CpuidReg::ECX, &mut entry.ecx),
+                (CpuidReg::EDX, &mut entry.edx),
+            ] {
+                // Lookup the adjustment corresponding to the entry's function/leaf and index/sub-leaf for each of the register.
+                let register_adjustments: Option<CpuidOutputRegisterAdjustments> =
+                    adjustments.iter().find_map(|(param, adjustment)| {
+                        ((param.leaf == entry.function)
+                            && param.sub_leaf.contains(&entry.index)
+                            && (param.register == reg))
+                            .then_some(*adjustment)
+                    });
+
+                match register_adjustments {
+                    Some(adjustment) => adjustment.adjust(reg_value),
+                    None => {
+                        // No matching cpuid parameters were found. We thus set the value of the register to 0.
+                        *reg_value = 0;
+                    }
+                }
+            }
+        }
+
+        Self::expected_entries_found(&cpuid, adjustments)?;
+        Ok(cpuid)
+    }
+
+    /// Check that we found every value that was supposed to be replaced with something else than 0
+    ///
+    /// IMPORTANT: This function assumes that the given `cpuid` has already been adjusted with the
+    /// provided `adjustments`.
+    fn expected_entries_found(
+        cpuid: &[CpuIdEntry],
+        adjustments: &[(CpuidParameters, Self)],
+    ) -> Result<(), MissingCpuidEntriesError> {
+        let mut missing_entry = false;
+
+        for (param, adjustment) in adjustments {
+            if adjustment.replacements == 0 {
+                continue;
+            }
+
+            if !cpuid.iter().any(|entry| {
+                (entry.function == param.leaf) && (param.sub_leaf.contains(&entry.index))
+            }) {
+                error!(
+                    "cannot adjust CPU profile. No entry found matching the required parameters: {param:?}"
+                );
+                missing_entry = true;
+            }
+        }
+        if missing_entry {
+            Err(MissingCpuidEntriesError)
+        } else {
+            Ok(())
+        }
+    }
+}