From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.14]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D679E13CA8A; Thu, 31 Oct 2024 04:56:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.14 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730350583; cv=none; b=NhlatDjoY6dJjnbPNKR+Ez9CLSR/twyCiI/OfYkR1gnJ1LvUF8SFYiLmtq1KWCoL0FBdV9wN4Y6sxzQ/2tJed6zcz50gh92wi/4mgPBgowXIfyT5GQQMpmjJaj/Cn7Ile6m5N8RpOIBAiOgA+cnktBg3lU1uemFhAI/LGcar1Xg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730350583; c=relaxed/simple; bh=flCsxwyjLE26j5Y/rFURu6azx7PHBiVzA7lT9R6aWno=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jqA++0Km3OFLuLGNltbikuW3DiMtLcRnCerc+Z5MMhLShmYs0nGbY1M/1nITxIgsuSIi9PANwH9swxZ13coHFHg4JCJiP0m/eZ9zYkw/uM0K2k4RnCrS7NnGCPwZH0Ti3Tinb3Ldzqf6grnHAxPsW2IxNCh2kw7ZGJsg0lcIa+w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=none smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=PQAlH1PV; arc=none smtp.client-ip=198.175.65.14 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="PQAlH1PV" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1730350582; x=1761886582; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=flCsxwyjLE26j5Y/rFURu6azx7PHBiVzA7lT9R6aWno=; b=PQAlH1PVNjPkF/GFCrTBeQd2CbapX86YRF3Msi0JanXtQgKVlDK0f3LZ y1W1TTnWhCwlKQKYjDs9nVdKfgprfd6MRE6XNFQ2qOB/5H7rz7OWE49Rr ZQjyIF04jiIHHe7XzoKWc1lkfy4DhfxvYYlInUtHRGjriBR0DfhDuoRtt b9K27vwI6YhCCDOW1I9uecUOaUcGFKKxEBa7Gc3uWt8dgp/e25pnd3qh5 uWPFFXePVJdDYi0GsVrOqMya54rCN/4WZTv47C1LZar7K1cK03TwnFL3B TCuZxUEwF1+R4lEQc+ECLN0yTdrN3PO5SV3vPE5m1EgWhzBUS9lg4o+yd g==; X-CSE-ConnectionGUID: NoyoBI+OQ/6NYnmqqD2neg== X-CSE-MsgGUID: oc1MAIenS6acsvs9lHBJYA== X-IronPort-AV: E=McAfee;i="6700,10204,11241"; a="33866738" X-IronPort-AV: E=Sophos;i="6.11,246,1725346800"; d="scan'208";a="33866738" Received: from fmviesa007.fm.intel.com ([10.60.135.147]) by orvoesa106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Oct 2024 21:56:20 -0700 X-CSE-ConnectionGUID: lA4uBXjaQHKh9JmtN8S87w== X-CSE-MsgGUID: aTI7/ZNRSrSJJBM/3DXaWg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.11,246,1725346800"; d="scan'208";a="82172371" Received: from unknown (HELO [10.238.12.149]) ([10.238.12.149]) by fmviesa007-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Oct 2024 21:56:17 -0700 Message-ID: <4734379d-97c4-44c8-ae40-be46da6e6239@linux.intel.com> Date: Thu, 31 Oct 2024 12:56:14 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/2] KVM: x86: Check hypercall's exit to userspace generically To: Sean Christopherson Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, isaku.yamahata@intel.com, rick.p.edgecombe@intel.com, kai.huang@intel.com, yuan.yao@linux.intel.com, xiaoyao.li@intel.com References: <20240826022255.361406-1-binbin.wu@linux.intel.com> <20240826022255.361406-2-binbin.wu@linux.intel.com> Content-Language: en-US From: Binbin Wu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/31/2024 4:49 AM, Sean Christopherson wrote: > On Mon, Aug 26, 2024, Binbin Wu wrote: >> Check whether a KVM hypercall needs to exit to userspace or not based on >> hypercall_exit_enabled field of struct kvm_arch. >> >> Userspace can request a hypercall to exit to userspace for handling by >> enable KVM_CAP_EXIT_HYPERCALL and the enabled hypercall will be set in >> hypercall_exit_enabled. Make the check code generic based on it. >> >> Signed-off-by: Binbin Wu >> Reviewed-by: Kai Huang >> --- >> arch/x86/kvm/x86.c | 5 +++-- >> arch/x86/kvm/x86.h | 4 ++++ >> 2 files changed, 7 insertions(+), 2 deletions(-) >> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index 966fb301d44b..e521f14ad2b2 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -10220,8 +10220,9 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu) >> cpl = kvm_x86_call(get_cpl)(vcpu); >> >> ret = __kvm_emulate_hypercall(vcpu, nr, a0, a1, a2, a3, op_64_bit, cpl); >> - if (nr == KVM_HC_MAP_GPA_RANGE && !ret) >> - /* MAP_GPA tosses the request to the user space. */ >> + /* Check !ret first to make sure nr is a valid KVM hypercall. */ >> + if (!ret && user_exit_on_hypercall(vcpu->kvm, nr)) > I don't love that the caller has to re-check for user_exit_on_hypercall(). Agree, it is not ideal. But if __kvm_emulate_hypercall() returns 0 to indicate user exit and 1 to indicate success, then the callers have to convert the return code to set return value for guest.  E.g., TDX code also needs to do the conversion. > I also don't love that there's a surprising number of checks lurking in > __kvm_emulate_hypercall(), e.g. that CPL==0, especially since the above comment > about "a valid KVM hypercall" can be intrepreted as meaning KVM is *only* checking > if the hypercall number is valid. > > E.g. my initial reaction was that we could add a separate path for userspace > hypercalls, but that would be subtly wrong. And my second reaction was to hoist > the common checks out of __kvm_emulate_hypercall(), but then I remembered that > the only reason __kvm_emulate_hypercall() is separate is to allow it to be called > by TDX with different source/destionation registers. > > So, I'm strongly leaning towards dropping the above change, squashing the addition > of the helper with patch 2, and then landing this on top. > > Thoughts? I have no strong preference and OK with the proposal below. Just some cases, which don't get the return value right as pointed by Kai in another thread. https://lore.kernel.org/kvm/3f158732a66829faaeb527a94b8df78d6173befa.camel@intel.com/ > > -- > Subject: [PATCH] KVM: x86: Use '0' in __kvm_emulate_hypercall() to signal > "exit to userspace" > > Rework __kvm_emulate_hypercall() to use '0' to indicate an exit to > userspace instead of relying on the caller to manually check for success > *and* if user_exit_on_hypercall() is true. Use '1' for "success" to > (mostly) align with KVM's de factor return codes, where '0' == exit to > userspace, '1' == resume guest, and -errno == failure. Unfortunately, > some of the PV error codes returned to the guest are postive values, so > the pattern doesn't exactly match KVM's "standard", but it should be close > enough to be intuitive for KVM readers. > > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/x86.c | 21 +++++++++++++++------ > 1 file changed, 15 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index e09daa3b157c..5fdeb58221e2 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -10024,7 +10024,7 @@ unsigned long __kvm_emulate_hypercall(struct kvm_vcpu *vcpu, unsigned long nr, > > switch (nr) { > case KVM_HC_VAPIC_POLL_IRQ: > - ret = 0; > + ret = 1; > break; > case KVM_HC_KICK_CPU: > if (!guest_pv_has(vcpu, KVM_FEATURE_PV_UNHALT)) > @@ -10032,7 +10032,7 @@ unsigned long __kvm_emulate_hypercall(struct kvm_vcpu *vcpu, unsigned long nr, > > kvm_pv_kick_cpu_op(vcpu->kvm, a1); > kvm_sched_yield(vcpu, a1); > - ret = 0; > + ret = 1; > break; > #ifdef CONFIG_X86_64 > case KVM_HC_CLOCK_PAIRING: > @@ -10050,7 +10050,7 @@ unsigned long __kvm_emulate_hypercall(struct kvm_vcpu *vcpu, unsigned long nr, > break; > > kvm_sched_yield(vcpu, a0); > - ret = 0; > + ret = 1; > break; > case KVM_HC_MAP_GPA_RANGE: { > u64 gpa = a0, npages = a1, attrs = a2; > @@ -10111,12 +10111,21 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu) > cpl = kvm_x86_call(get_cpl)(vcpu); > > ret = __kvm_emulate_hypercall(vcpu, nr, a0, a1, a2, a3, op_64_bit, cpl); > - if (nr == KVM_HC_MAP_GPA_RANGE && !ret) > - /* MAP_GPA tosses the request to the user space. */ > + if (!ret) > return 0; > > - if (!op_64_bit) > + /* > + * KVM's ABI with the guest is that '0' is success, and any other value > + * is an error code. Internally, '0' == exit to userspace (see above) > + * and '1' == success, as KVM's de facto standard return codes are that > + * plus -errno == failure. Explicitly check for '1' as some PV error > + * codes are positive values. > + */ I didn't understand the last sentence: "Explicitly check for '1' as some PV error codes are positive values." The functions called in __kvm_emulate_hypercall() for PV features return -KVM_EXXX for error code. Did you mean the functions like kvm_pv_enable_async_pf(), which return 1 for error, would be called in __kvm_emulate_hypercall() in the future? If this is the concern, then we cannot simply convert 1 to 0 then. > + if (ret == 1) > + ret = 0; > + else if (!op_64_bit) > ret = (u32)ret; > + > kvm_rax_write(vcpu, ret); > > return kvm_skip_emulated_instruction(vcpu); > > base-commit: 675248928970d33f7fc8ca9851a170c98f4f1c4f