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Wanpeng Li 41e1386388 KVM: MMU: Fix infinite loop when there is no available mmu page 
commit ed52870f46 upstream.

The below test case can cause infinite loop in kvm when ept=0.

    #include <unistd.h>
    #include <sys/syscall.h>
    #include <string.h>
    #include <stdint.h>
    #include <linux/kvm.h>
    #include <fcntl.h>
    #include <sys/ioctl.h>

    long r[5];
    int main()
    {
    	r[2] = open("/dev/kvm", O_RDONLY);
    	r[3] = ioctl(r[2], KVM_CREATE_VM, 0);
    	r[4] = ioctl(r[3], KVM_CREATE_VCPU, 7);
    	ioctl(r[4], KVM_RUN, 0);
    }

It doesn't setup the memory regions, mmu_alloc_shadow/direct_roots() in
kvm return 1 when kvm fails to allocate root page table which can result
in beblow infinite loop:

    vcpu_run() {
    	for (;;) {
	    	r = vcpu_enter_guest()::kvm_mmu_reload() returns 1
	    	if (r <= 0)
	    		break;
	    	if (need_resched())
	    		cond_resched();
      }
    }

This patch fixes it by returning -ENOSPC when there is no available kvm mmu
page for root page table.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Fixes: 26eeb53cf0 (KVM: MMU: Bail out immediately if there is no available mmu page)
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2017-12-29 17:53:48 +01:00
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README 

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.