disabling apic Interrupts by modify the tpr in the kernel

NTDEV
1

i know there high_level irql to disable all interrupts i want to know if its possible to do so on apic

// I’ve discovered that the APIC base address must be mapped to virtual memory to ensure proper access

is this approach correct?

#include <intrin.h>
#include <wdm.h>

#define IA32_APIC_BASE_MSR 0x1B
#define APIC_TPR_OFFSET 0x80

uintptr_t cpu_get_apic_base() {
    uint64_t msrValue = __readmsr(IA32_APIC_BASE_MSR);
  
#ifdef __PHYSICAL_MEMORY_EXTENSION__
    return msrValue & 0xFFFFFFFFFFFFF000ULL;
#else
    return msrValue & 0xFFFFF000;
#endif
}

uintptr_t map_physical_to_virtual(uint64_t phys_addr, SIZE_T size) {
    PHYSICAL_ADDRESS PhysicalAddress;
    PhysicalAddress.QuadPart = phys_addr;
    return (uintptr_t)MmMapIoSpace(PhysicalAddress, size, MmNonCached);
}

void unmap_virtual_address(void* virt_addr) {
    MmUnmapIoSpace(virt_addr, sizeof(uint32_t)); 
}

static inline uint32_t read_tpr(uintptr_t apicBaseVirt) {
    return *((volatile uint32_t*)(apicBaseVirt + APIC_TPR_OFFSET));
}

static inline void write_tpr(uintptr_t apicBaseVirt, uint32_t value) {
    *((volatile uint32_t*)(apicBaseVirt + APIC_TPR_OFFSET)) = value;
}

void DisableAndEnableApicInterrupts() {
    uint64_t apicBasePhys = cpu_get_apic_base();
    uintptr_t apicBaseVirt = map_physical_to_virtual(apicBasePhys, sizeof(uint32_t));
    if (!apicBaseVirt) {
       DbgPrint("Couldn't map physical memory.\n");
        return;
    }
    
    uint32_t original_tpr = read_tpr(apicBaseVirt);
    
    // Raise the APIC's task priority to effectively mask off all interrupts
    write_tpr(apicBaseVirt, 0xFF);

    // ... Your code that needs to run without external interrupts ...

    // Restore the original TPR value to re-enable interrupts
    write_tpr(apicBaseVirt, original_tpr);

    unmap_virtual_address((void*)apicBaseVirt);
}
2

Why would you want to do this? Seriously… it assumes a given system hardware configuration… it’s not any sort of “real” solution to any “real” problem… This is some sort of playing around experiment??

Peter

3

not at all i found some guy did the same but on PIC
https://groups.google.com/g/comp.os.ms-windows.programmer.nt.kernel-mode/c/x1zirZabBVk/m/e2mo5GlcsBwJ

so i was wondering if its also possible on APIC

4

mission accomplished thread can be closed :slight_smile: