On 01/06/2017 10:56, Roman Pen wrote:
> This is a fix for the problem [1], where VMCB.CPL was set to 0 and interrupt
> was taken on userspace stack. The root cause lies in the specific AMD CPU
> behaviour which manifests itself as unusable segment attributes on SYSRET[2].
>
> Here in this patch flags are not touched even segment is unusable or is not
> present, therefore CPL (which is stored in DPL field) should not be lost and
> will be successfully restored on kvm/svm kernel side.
>
> Also current patch should not break desired behavior described in this commit:
>
> 4cae9c97967a ("target-i386: kvm: clear unusable segments' flags in migration")
>
> since present bit will be dropped if segment is unusable or is not present.
>
> This is the second part of the whole fix of the corresponding problem [1],
> first part is related to kvm/svm kernel side and does exactly the same:
> segment attributes are not zeroed out.
>
> [1] Message id:
> CAJrWOzD6Xq==b-zYCDdFLgSRMPM-NkNuTSDFEtX=7mret45...@mail.gmail.com
> [2] Message id:
> 5d120f358612d73fc909f5bfa47e7bd082db0af0.1429841474.git.l...@kernel.org
>
> Signed-off-by: Roman Pen <roman.peny...@profitbricks.com>
> Signed-off-by: Mikhail Sennikovskii <mikhail.sennikovs...@profitbricks.com>
> Cc: Paolo Bonzini <pbonz...@redhat.com>
> Cc: Rddadim Krčmář <rkrc...@redhat.com>
> Cc: Michael Chapman <m...@very.puzzling.org>
> Cc: qemu-devel@nongnu.org
> ---
> target/i386/kvm.c | 20 ++++++++------------
> 1 file changed, 8 insertions(+), 12 deletions(-)
Queued, thanks.
Paolo
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index 011d4a55b136..faee904d9d59 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -1300,18 +1300,14 @@ static void get_seg(SegmentCache *lhs, const struct
> kvm_segment *rhs)
> lhs->selector = rhs->selector;
> lhs->base = rhs->base;
> lhs->limit = rhs->limit;
> - if (rhs->unusable) {
> - lhs->flags = 0;
> - } else {
> - lhs->flags = (rhs->type << DESC_TYPE_SHIFT) |
> - (rhs->present * DESC_P_MASK) |
> - (rhs->dpl << DESC_DPL_SHIFT) |
> - (rhs->db << DESC_B_SHIFT) |
> - (rhs->s * DESC_S_MASK) |
> - (rhs->l << DESC_L_SHIFT) |
> - (rhs->g * DESC_G_MASK) |
> - (rhs->avl * DESC_AVL_MASK);
> - }
> + lhs->flags = (rhs->type << DESC_TYPE_SHIFT) |
> + ((rhs->present && !rhs->unusable) * DESC_P_MASK) |
> + (rhs->dpl << DESC_DPL_SHIFT) |
> + (rhs->db << DESC_B_SHIFT) |
> + (rhs->s * DESC_S_MASK) |
> + (rhs->l << DESC_L_SHIFT) |
> + (rhs->g * DESC_G_MASK) |
> + (rhs->avl * DESC_AVL_MASK);
> }
>
> static void kvm_getput_reg(__u64 *kvm_reg, target_ulong *qemu_reg, int set)
>
