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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id y16-20020a17090a6c9000b001c993d935e7sm245836pjj.56.2022.04.04.12.54.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 Apr 2022 12:54:33 -0700 (PDT) Date: Mon, 4 Apr 2022 19:54:29 +0000 From: Sean Christopherson To: "Maciej S. Szmigiero" Cc: Maxim Levitsky , Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 5/8] KVM: SVM: Re-inject INT3/INTO instead of retrying the instruction Message-ID: References: <20220402010903.727604-1-seanjc@google.com> <20220402010903.727604-6-seanjc@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 04, 2022, Sean Christopherson wrote: > On Mon, Apr 04, 2022, Maciej S. Szmigiero wrote: > > > > > index 47e7427d0395..a770a1c7ddd2 100644 > > > > > --- a/arch/x86/kvm/svm/svm.h > > > > > +++ b/arch/x86/kvm/svm/svm.h > > > > > @@ -230,8 +230,8 @@ struct vcpu_svm { > > > > > bool nmi_singlestep; > > > > > u64 nmi_singlestep_guest_rflags; > > > > > - unsigned int3_injected; > > > > > - unsigned long int3_rip; > > > > > + unsigned soft_int_injected; > > > > > + unsigned long soft_int_linear_rip; > > > > > /* optional nested SVM features that are enabled for this guest */ > > > > > bool nrips_enabled : 1; > > > > > > > > > > > > I mostly agree with this patch, but think that it doesn't address the > > > > original issue that Maciej wanted to address: > > > > > > > > Suppose that there is *no* instruction in L2 code which caused the software > > > > exception, but rather L1 set arbitrary next_rip, and set EVENTINJ to software > > > > exception with some vector, and that injection got interrupted. > > > > > > > > I don't think that this code will support this. > > > > > > Argh, you're right. Maciej's selftest injects without an instruction, but it doesn't > > > configure the scenario where that injection fails due to an exception+VM-Exit that > > > isn't intercepted by L1 and is handled by L0. The event_inj test gets the coverage > > > for the latter, but always has a backing instruction. > > > > Still reviewing the whole patch set, but want to clear this point quickly: > > The selftest does have an implicit intervening NPF (handled by L0) while > > injecting the first L1 -> L2 event. > > I'll do some debug to figure out why the test passes for me. I'm guessing I either > got lucky, e.g. IDT was faulted in already, or I screwed up and the test doesn't > actually pass. Well that was easy. My code is indeed flawed and skips the wrong instruction, the skipped instruction just so happens to be a (spurious?) adjustment of RSP. The L2 guest function never runs to completion and so the "bad" RSP is never consumed. KVM: incomplete injection for L2, vector 32 @ 401c70. next_rip = 0 KVM: injecting for L2, vector 0 @ 401c70. next_rip = 401c74 0000000000401c70 : 401c70: 48 83 ec 08 sub $0x8,%rsp 401c74: 83 3d 75 a7 0e 00 01 cmpl $0x1,0xea775(%rip) # 4ec3f0 401c7b: 74 1e je 401c9b 401c7d: 45 31 c0 xor %r8d,%r8d 401c80: b9 32 00 00 00 mov $0x32,%ecx 401c85: ba 90 40 4b 00 mov $0x4b4090,%edx 401c8a: 31 c0 xor %eax,%eax 401c8c: be 02 00 00 00 mov $0x2,%esi 401c91: bf 02 00 00 00 mov $0x2,%edi 401c96: e8 05 ae 00 00 call 40caa0 401c9b: 0f 01 d9 vmmcall 401c9e: 0f 0b ud2 401ca0: 83 3d 4d a7 0e 00 01 cmpl $0x1,0xea74d(%rip) # 4ec3f4 401ca7: 74 1e je 401cc7 401ca9: 45 31 c0 xor %r8d,%r8d 401cac: b9 36 00 00 00 mov $0x36,%ecx 401cb1: ba b8 40 4b 00 mov $0x4b40b8,%edx 401cb6: 31 c0 xor %eax,%eax 401cb8: be 02 00 00 00 mov $0x2,%esi 401cbd: bf 02 00 00 00 mov $0x2,%edi 401cc2: e8 d9 ad 00 00 call 40caa0 401cc7: f4 hlt 401cc8: 48 83 c4 08 add $0x8,%rsp 401ccc: c3 ret 401ccd: 0f 1f 00 nopl (%rax) I don't see why the compiler is creating room for a single variable, but it doesn't really matter, the easiest way to detect this bug is to assert that the return RIP in the INT 0x20 handler points at l2_guest_code, e.g. this fails: diff --git a/tools/testing/selftests/kvm/x86_64/svm_nested_soft_inject_test.c b/tools/testing/selftests/kvm/x86_64/svm_nested_soft_inject_test.c index d39be5d885c1..257aa2280b5c 100644 --- a/tools/testing/selftests/kvm/x86_64/svm_nested_soft_inject_test.c +++ b/tools/testing/selftests/kvm/x86_64/svm_nested_soft_inject_test.c @@ -40,9 +40,13 @@ static void guest_bp_handler(struct ex_regs *regs) } static unsigned int int_fired; +static void l2_guest_code(void); + static void guest_int_handler(struct ex_regs *regs) { int_fired++; + GUEST_ASSERT_2(regs->rip == (unsigned long)l2_guest_code, + regs->rip, (unsigned long)l2_guest_code); } static void l2_guest_code(void)