Re: [PATCH] tcg/svm: use host cr4 during NPT page table walk

[Paolo Bonzini]

On 29/06/20 15:25, Alexander Boettcher wrote:
> Hello,
> 
> during a page table walk of TCG+SVM the code in target/i386/excp_helper.c 
> get_hphys() uses the cr4 register of the guest instead of the hypervisor to 
> check for the PSE bit. In the test case we have, the guest have not enabled 
> (yet) the PSE bit and so the page table walk results in a wrong host physical 
> address resolution and wrong content read by the guest.
> 
> Attached patch is against 4.2.1, but works also on 3.1.0. It fixes the issue 
> for our automated testcase, which is a 32bit hypervisor w/o PAE support 
> running a guest VM with tcg+svm.
> The test worked beforehand up to qemu 2.12, started to fail with qemu 3.0 and 
> later. The added TCG/SVM NPT commit seems to introduce the regression.
> 
> In case someone want to try to reproduce it, the iso is at [0], the good case 
> is [1] and the failing case is [2]. The used commandline is:
> 
> qemu-system-i386 -no-kvm -nographic -cpu phenom -m 512 -machine q35 -cdrom 
> seoul-vmm-test.iso
> 
> [0] https://depot.genode.org/alex-ab/images/seoul-vmm-test.iso
> [1] https://depot.genode.org/alex-ab/images/seoul-vmm-good.txt
> [2] https://depot.genode.org/alex-ab/images/seoul-vmm-bad.txt
> 

Queued, thanks.

Paolo