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Packet receive interrupts are disabled. The driver provides a poll method to the kernel. That method will fetch all incoming packets available, on the network card or a DMA ring, so that they will then be handled by the kernel. When allowed to, the kernel calls the device poll method to possibly handle many packets at once.
The interrupt priority level (IPL) is a part of the current system interrupt state, which indicates the interrupt requests that will currently be accepted. The IPL may be indicated in hardware by the registers in a programmable interrupt controller , or in software by a bitmask or integer value and source code of threads.
Ideally, only highly trusted kernel code is allowed to execute in the unrestricted mode; everything else (including non-supervisory portions of the operating system) runs in a restricted mode and must use a system call (via interrupt) to request the kernel perform on its behalf any operation that could damage or compromise the system, making it ...
In systems that support privileged mode, only privileged applications (usually the OS kernel) may modify the Interrupt flag. In an x86 system this only applies to protected mode code (Real mode code may always modify the Interrupt flag). CLI and STI are privileged instructions, which cause a general protection fault if an unprivileged ...
When an interrupt occurs, the processor multiplies the interrupt vector by the entry size (8 for protected mode, 16 for long mode) and adds the result to the IDT base address. [4] If the address is inside the table, the DPL is checked and the interrupt is handled based on the gate type.
In computer systems programming, an interrupt handler, also known as an interrupt service routine or ISR, is a special block of code associated with a specific interrupt condition. Interrupt handlers are initiated by hardware interrupts, software interrupt instructions, or software exceptions , and are used for implementing device drivers or ...
The SMM can only be entered through SMI (System Management Interrupt). The processor executes the SMM code in a separate address space (SMRAM) that has to be made inaccessible to other operating modes of the CPU by the firmware. [7] System Management Mode can address up to 4 GB memory as huge real mode.
Furthermore, on a modern x86 system, BIOS calls can only be performed in Real mode, or Virtual 8086 mode. v8086 is not an option in Long mode. This means that a modern operating system, which operates in Protected mode (32 bit), or Long mode (64 bit), would need to switch into real mode and back to call the BIOS - a hugely expensive operation.