From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f73.google.com (mail-pj1-f73.google.com [209.85.216.73]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 50E022F3C03 for ; Fri, 12 Dec 2025 17:53:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.73 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765562003; cv=none; b=EjaO3c9w8H01XJoXQ236YXhisvKwwLOAO7quRvjP4GQhg7JEG5laHHKysgrVMhFMbO5HRe7TzNfNhIYBPWextCEaRZ/l57HgJEStjkLZAeBBXqRznoV1dChSSexq/CcEX/EcnQ5SfM+Q1b4oSjCM69QaBkaZMXr37mCYUhSEEAs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765562003; c=relaxed/simple; bh=SBY5iBtKi33UI4o709keo90W1kQlSEb3hKaGV2YCfAI=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=djSvImGHO3pgOv00XieOYCGwHjb3cH1ZNo/E7P4VBsyPWv1ViE+dcX8wMqmcD49OEP+ERBXE2OkmbEHK7L/n3HweWBOFKIEFfFsCbFswqIKwGch+Sh+8rPZyxuBFS1l/PAg7Zxn+mveJewvYuRyLDTxcX6wvHbY84fPlBwh3JwQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=NhCOYK9m; arc=none smtp.client-ip=209.85.216.73 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="NhCOYK9m" Received: by mail-pj1-f73.google.com with SMTP id 98e67ed59e1d1-341616a6fb7so1549725a91.0 for ; Fri, 12 Dec 2025 09:53:22 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1765562002; x=1766166802; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=V2Cj0aGGug40IgYm+TDWR1qUdjJrq2iLmar2qhOggec=; b=NhCOYK9mgxYKyTyhPO7ytGBIgLnVtZMtPxsYAMzR0F6JhY+39BOSDKZXS10Q/NyJpX xWB2YkFlaW073tjPY9Bsm8hRmX3hOddz60B/jTeaFdO9cvBrhICPKLc+yOgWlBkf+imv Uyn8Jq7ZTyZ7xGrFY5VHESzywke8VZ9Kq//33lc1vt1+htEQOejm/zzZYV6LYEgBXeOB +15AnezbOZ15TgRiN6QKHDlw61gD8NwoBroOCrk4povDLy01WXaEo7Ew+QkSWrYtPbgT u4tX4HXnrwkVkVghCv2RZLb3Y8BiVecGImZfaFVHm0UXxGflAIi4BlTs6A0jtmRjB0OT jEPA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1765562002; x=1766166802; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=V2Cj0aGGug40IgYm+TDWR1qUdjJrq2iLmar2qhOggec=; b=oTyU3OMLVM1VhXKrI0yaEglyTH15gv75QHxEkTxacF8w+5pCocpysTypbU3uQ5CkjT qvg14k4YS7n+IQCYeZkRqliKDoFSJUbnJ6JiK5quwj6AgTbU8Do3A0cpyfDl2csna13i hTpGnulgaQhlfndhR4rY2oK291hQ5ofj5L2kFZuvVFXakfiUcX9wX48E4wLwSyjpqiYC 4DOhqwryx662DNqkZHtpADMUZXxB9ikOYotT5qpxXQK4kpjM2/mCIK28BN2Ka7f+AIbE 6IprFGVnoiVYbzNurvtcimuDWV/R2UWOxAzAkx8FLOg0PY7m0EeYtpPnFO9QjpkMW/AL vvUA== X-Gm-Message-State: AOJu0Yw2/fho2BSWgg6q3gUI2qPB5UCUzIDq5Dn7Xia7DnuRt1xSnJD9 H7s2lm1f3LwkzDSGiGSejmQb0ZCGEmsfi6dM31bueUFZso/puiMQhuK4WzkCAH6eEwJ5uOur63H /OBTqyA== X-Google-Smtp-Source: AGHT+IE+fRP2zd2rUtse8AQMH2CveeUHlAeg8i9qQSHKAEZVSRaAflZLwfBqY+Fzjr3Dzfq/m276ap32cng= X-Received: from pjbqe8.prod.google.com ([2002:a17:90b:4f88:b0:349:3867:ccc1]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:2b46:b0:340:b501:7b7d with SMTP id 98e67ed59e1d1-34abd7bf548mr2551895a91.14.1765562001624; Fri, 12 Dec 2025 09:53:21 -0800 (PST) Date: Fri, 12 Dec 2025 09:53:20 -0800 In-Reply-To: <20251212094647.GA65305@k08j02272.eu95sqa> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <45cbc005e14ea2a4b9ec803a91af63e364aeb71a.1757416809.git.houwenlong.hwl@antgroup.com> <20251211140520.GC42509@k08j02272.eu95sqa> <20251212094647.GA65305@k08j02272.eu95sqa> Message-ID: Subject: Re: [PATCH 4/7] KVM: x86: Consolidate KVM_GUESTDBG_SINGLESTEP check into the kvm_inject_emulated_db() From: Sean Christopherson To: Hou Wenlong Cc: kvm@vger.kernel.org, Lai Jiangshan , Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Fri, Dec 12, 2025, Hou Wenlong wrote: > On Thu, Dec 11, 2025 at 09:19:39AM -0800, Sean Christopherson wrote: > > On Thu, Dec 11, 2025, Hou Wenlong wrote: > > +static noinline unsigned long singlestep_with_code_db(void) > > +{ > > + unsigned long start; > > + > > + asm volatile ( > > + "lea 1f(%%rip), %0\n\t" > > + "mov %0, %%dr2\n\t" > > + "mov $" xstr(DR7_FIXED_1 | DR7_EXECUTE_DRx(2) | DR7_GLOBAL_ENABLE_DR2) ", %0\n\t" > > + "mov %0, %%dr7\n\t" > > + "pushf\n\t" > > + "pop %%rax\n\t" > > + "or $(1<<8),%%rax\n\t" > > + "push %%rax\n\t" > > + "popf\n\t" > > + "and $~(1<<8),%%rax\n\t" > In my previous understanding, I thought there would be two #DBs > generated at the instruction boundary. First, the single-step trap #DB > would be handled, and then, when resuming to start the new instruction, > it would check for the code breakpoint and generate a code fault #DB. > However, it turns out that the check for the code breakpoint happened > before the instruction boundary. Yeah, that's what I was trying to explain by describing code breakpoint as fault-like. > I also see in the kernel hardware breakpoint handler that it notes that code > breakpoints and single-step can be detected together. Is this due to > instruction prefetch? Nope, it's just how #DBs work, everything pending gets smushed together. Note, data #DBs can also be coincident. E.g. it's entirely possible that you could observe a code breakpoint, a data breakpoint, and a single-step breakpoint in a single #DB. > If we want to emulate the hardware behavior in the emulator, does that > mean we need to check for code breakpoints in kvm_vcpu_do_single_step() > and set the DR_TRAP_BITS along with the DR6_BS bit? Hmm, ya, I think so? I don't think the CPU will fetch and merge the imminent code #DB with the injected single-step #DB.