From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [patch] KVM: always reload segment selectors Date: Sun, 11 Mar 2007 15:04:08 +0200 Message-ID: <45F3FE48.2040808@qumranet.com> References: <20070311122441.GA10774@elte.hu> <45F3F85D.7000509@qumranet.com> <20070311124146.GA15115@elte.hu> <20070311125233.GA17328@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Ingo Molnar Return-path: In-Reply-To: <20070311125233.GA17328-X9Un+BFzKDI@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Ingo Molnar wrote: > Subject: [patch] KVM: always reload segment selectors > From: Ingo Molnar > > failed VM entry on VMX might still change %fs or %gs, thus make sure > that KVM always reloads the segment selectors. This is crutial on both > x86 and x86_64: x86 has __KERNEL_PDA in %fs on which things like > 'current' depends and x86_64 has 0 there and needs MSR_GS_BASE to work. > > Signed-off-by: Ingo Molnar > --- > drivers/kvm/vmx.c | 37 +++++++++++++++++++++---------------- > 1 file changed, 21 insertions(+), 16 deletions(-) > > Index: linux/drivers/kvm/vmx.c > =================================================================== > --- linux.orig/drivers/kvm/vmx.c > +++ linux/drivers/kvm/vmx.c > @@ -1896,6 +1896,27 @@ again: > [cr2]"i"(offsetof(struct kvm_vcpu, cr2)) > : "cc", "memory" ); > > + /* > + * Reload segment selectors ASAP. (it's needed for a functional > + * kernel: x86 relies on having __KERNEL_PDA in %fs and x86_64 > + * relies on having 0 in %gs for the CPU PDA to work.) > + */ > + if (fs_gs_ldt_reload_needed) { > + load_ldt(ldt_sel); > + load_fs(fs_sel); > + /* > + * If we have to reload gs, we must take care to > + * preserve our gs base. > + */ > + local_irq_disable(); > + load_gs(gs_sel); > +#ifdef CONFIG_X86_64 > + wrmsrl(MSR_GS_BASE, vmcs_readl(HOST_GS_BASE)); > +#endif > + local_irq_enable(); > + > + reload_tss(); > + } > ++kvm_stat.exits; > > save_msrs(vcpu->guest_msrs, NR_BAD_MSRS); btw, looking at the code, we could just remove fs from the fs_gs_reload_needed and make in unconditional. VT knows how to reload segments, except if they're user segments (groan). In the case of fs, if it's used for the pda, it's obviously a kernel segment. gs is different: since only the segment base is loaded (via swapgs), the selector part could well be a userspace selector, and thus the irq-protected reload is needed. Anyway, I'm applying the patch as the above discourse is irrelevant to the fix. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV