VRoom A high end RISC-V implementation
The presentation was interesting; but I would like to write an idea that is tangentially related to this CPU.<p>I noticed that modern CPUs are optimized for legacy monolith OS kernels like Linux or Windows. But having a large, multimegabyte kernel is a bad idea from a security standpoint. A single mistake or intentional error in some rarely used component (like a temperature sensor driver) can get attacker full access to the system. Again, an error in any part of the monolith kernel can cause system failure. And Linux kernel doesn&#x27;t even use static analysis to find bugs! It is obvious that using microkernels could solve many of the issues above.<p>But microkernels tend to have poor performance. One of the reasons for this could be high context switch latency. CPUs with high context switch latency are only good for legacy OSes and not ready for better future kernels. Therefore, either we will find a way to make context switches fast or we will have to stay with large, insecure kernels full of vulnerabilities.<p>So I was thinking what could be done here. For example, one thing that could be improved is to get rid of address space switch. It causes flushes of various caches and it hurts performance. Instead, we could always use the single mapping from virtual to physical addresses, but allocate each process different virtual address range. To implement this, we could add two registers, which would hold minumum and maximum accessible virtual addresses. It should be easy to check the address against them to prevent speculative out of bounds memory accesses.<p>By the way, 32-bit x86 architecture had segments, that could be used to divide single address space between processes.<p>Another thing that can take time is saving&#x2F;restoring registers on context switch. One way to solve the problem could be to use multiple banks (say, 64 banks) of registers that can be quickly switched, another way would be to zero out registers on return from kernel and let processes save them if they need it.<p>Or am I wrong somewhere and fast context switches cannot be implemented this way?