From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [patch 3/3] KVM: VMX: handle segment limit granularity special case in software Date: Thu, 17 Jul 2008 16:20:38 +0300 Message-ID: <487F4726.5030906@qumranet.com> References: <20080716220709.886199616@localhost.localdomain> <20080716221401.578260549@localhost.localdomain> <487F190D.3090701@qumranet.com> <20080717124326.GA7566@dmt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Marcelo Tosatti Return-path: Received: from il.qumranet.com ([212.179.150.194]:26629 "EHLO il.qumranet.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758380AbYGQNUk (ORCPT ); Thu, 17 Jul 2008 09:20:40 -0400 In-Reply-To: <20080717124326.GA7566@dmt.cnet> Sender: kvm-owner@vger.kernel.org List-ID: Marcelo Tosatti wrote: > On Thu, Jul 17, 2008 at 01:03:57PM +0300, Avi Kivity wrote: > >> Marcelo Tosatti wrote: >> >>> As the comment in the diff mentions, VMX does not accept any bit in >>> the range 11:0 of ES,CS,FS,GS,SS segment registers limit field to be >>> zero with the granulity bit set to one. >>> >>> So clear granularity and adjust the limit accordingly. >>> >>> Signed-off-by: Marcelo Tosatti >>> >>> Index: kvm/arch/x86/kvm/vmx.c >>> =================================================================== >>> --- kvm.orig/arch/x86/kvm/vmx.c >>> +++ kvm/arch/x86/kvm/vmx.c >>> @@ -1665,6 +1665,22 @@ static void vmx_set_segment(struct kvm_v >>> return; >>> } >>> vmcs_writel(sf->base, var->base); >>> + >>> + /* >>> + * section 22.3.1.2: >>> + * - If any bit in the limit field in the range 11:0 is 0, G must be 0. >>> + * - If any bit in the limit field in the range 31:20 is 1, G must be 1. >>> + */ >>> + if (!vcpu->arch.rmode.active && !var->unusable && >>> + seg != VCPU_SREG_TR && seg != VCPU_SREG_LDTR) { >>> +#define SEG_MASK ((1 << 12)-1) >>> + if (var->g && (var->limit & SEG_MASK) != SEG_MASK) { >>> + var->g = 0; >>> + var->limit <<= 12; >>> + var->limit |= SEG_MASK; >>> + } >>> + } >>> + >>> >> Both kvm_segment::limit and vmx's GUEST_xS_LIMIT are normalized (always >> in bytes), so I don't see why you are modifying var->limit (which is an >> input parameter!) >> > > > The problem is the Windows new TSS's FS segment: > > unhandled vm exit: 0x80000021 vcpu_id 2 > rax 0000000000000000 rbx 0000000000000000 rcx 0000000000000000 rdx > 0000000000000000 > rsi 0000000000000000 rdi 0000000000000000 rsp 00000000fd6b73c0 rbp > 0000000000000000 > r8 0000000000000000 r9 0000000000000000 r10 0000000000000000 r11 > 0000000000000000 > r12 0000000000000000 r13 0000000000000000 r14 0000000000000000 r15 > 0000000000000000 > rip 000000008088ab72 rflags 00004002 > cs 0008 (00000000/000fffff p 1 dpl 0 db 1 s 1 type b l 0 g 1 avl 0) > ds 0023 (00000000/000fffff p 1 dpl 3 db 1 s 1 type 3 l 0 g 1 avl 0) > es 0023 (00000000/000fffff p 1 dpl 3 db 1 s 1 type 3 l 0 g 1 avl 0) > ss 0010 (00000000/000fffff p 1 dpl 0 db 1 s 1 type 3 l 0 g 1 avl 0) > fs 0030 (fffffffffd6b1000/00000001 p 1 dpl 0 db 1 s 1 type 3 l 0 g 1 avl > ^^^^^^^ ^^^ > > "section 22.3.1.2: > - If any bit in the limit field in the range 11:0 is 0, G must be 0." > > So this patch fixes that particular issue by setting G to 0 (G=1 ignores > the 12 least significant bits of the offset when comparing the address > against the segment limit), then shifts left the limit by 12, and sets > those 12 bits. > > I don't understand what you mean by "vmx's GUEST_sX_LIMIT are > normalized". > > I meant, they are always in bytes. In a descriptor, the limit is in bytes or pages, depending on the g bit. > Do you have a better suggestion on how to deal with this? Or is it > supposed to by handled somewhere already? I think the problem is in seg_desct_to_kvm_desct() (besides the extra T's). It copies the limit from the descriptor directly to the kvm_segment structure. Most likely a simple if (seg_desc->g) kvm_desct->limit <<= 12; will suffice. -- error compiling committee.c: too many arguments to function