From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f202.google.com (mail-pf1-f202.google.com [209.85.210.202]) (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 0B4D186127 for ; Thu, 8 Feb 2024 17:27:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707413227; cv=none; b=TZ46vGLMrCGy2TwZId3RUO691PkMUOhkgW5rjkIcl7FP9U9m7WqYysMuMlS23eFlz4ULjT0ijYAj0KshH8JVrFMdaGK6+wEoyffLACa1bPgDGE635P6yEFPax549oDAlFZ5GNimr5bp4Mzx0LuFIT/VtafqywPnUHyGCHGO9k7Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707413227; c=relaxed/simple; bh=sx6KhQk9Is/4dxTU8a0rjN3JOBcYjPFn14qRnNkA5SY=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=m0bDt3AVujfCpxtwEX45aaW8GvZtJt8MQyHyuj4h9WQIb+RPZzimhJjv36EayjwVT68Fu8loKVEuydP2DJJcZGkfylUIi+197qzJBj9LdD04KPDsTpBwPcwiNvvcIPMpZyBBamdWc2dIjYyNCLIq9cbC8ndkpwtmn+TDSavIQCM= 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=Gn175dGl; arc=none smtp.client-ip=209.85.210.202 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="Gn175dGl" Received: by mail-pf1-f202.google.com with SMTP id d2e1a72fcca58-6e04e1ac036so57548b3a.3 for ; Thu, 08 Feb 2024 09:27:04 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1707413224; x=1708018024; 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=gBwp2cY+kDK1oMSufcYCS0Brw297vTH+3c3ODiiUoog=; b=Gn175dGli9LztjZ+EVogEBA46VYuRBuiuZ4zQYf0EVSw8NFYfO/rGT1H8cFWX/5aVE U1ykf89PUDhWzmLxcblWZIpkvewo+/sszS80JcQnsl0vOX1+2MejjTBe2rU0fa2lR2/+ qPAPbn5+weGildRfWjvYbrsrKP8OybaRpOVE5hQ+beBS6nuUkj8R2XSAOLvnoqiL++MC cNjBWWFIGPR9wmoxqOFw7FQvMur61sOxID6kjJqQkv0MOK+y6P3UMawwO6D1tJ44boJn 6RDI0Fd00H2tx1CEIXuRVnqo0h7+AZbSi2HVbEazMVZzLd1SS6KPJvDMFWlpRVb3cx0Q NCiA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1707413224; x=1708018024; 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=gBwp2cY+kDK1oMSufcYCS0Brw297vTH+3c3ODiiUoog=; b=PHQRnkMSDHbzZTaNlmZQYcbc0xp6PQjcB/5IyvlhpSWsxlpanHgaJyte8DRrKGWaFK iUgDe8sqlGOM+IkgjwI22uaiqKFx2cHGwpeiiByRQ6xJcppOeKjbFHGvh4FV1htGG4Yd 5gk6VsMG3gzXU6d/HFr9mpiCJyWvqb6nBpy3M9DiJfcK4CjvV1GbJOdy+12wjqmRtrTx EnTGoPKglBDJHIGt7LPmn6Ah2KTgeouVwogq4AEsQui4zoSY1dGUuzkGuoxYNvxxYadv nVyIH7FletZ0WSVrFG9xgYA+f25lwxy2RB2uj2K04/pKirnhrqZoOn86aq8ZBkRFZt5U 5wjg== X-Gm-Message-State: AOJu0Yw1HvHYtPtpKBpkcTsOyvlU7iiEGdHPGSb9bPTWIuvhFSLpNUFJ wSsyIAXLUr37JPjjFlWQ8++tjR+/veLxoSQnIeJDK6d5x2CwA7kei2HETrC7DjzrBKxPc1mm77E CPw== X-Google-Smtp-Source: AGHT+IF6y2Fj9Q0xzklv4qNxJB4M0iqYnYF4z+RAImjVdV5uh7OyzZLHK0LW86J/FLUDUS/+nQQagI/rkCc= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:6a00:2281:b0:6df:e3d1:dd0f with SMTP id f1-20020a056a00228100b006dfe3d1dd0fmr365573pfe.4.1707413224273; Thu, 08 Feb 2024 09:27:04 -0800 (PST) Date: Thu, 8 Feb 2024 09:27:02 -0800 In-Reply-To: <20240208002420.34mvemnzrwwsaesw@amd.com> Precedence: bulk X-Mailing-List: linux-crypto@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20231016115028.996656-1-michael.roth@amd.com> <20231016115028.996656-9-michael.roth@amd.com> <20240208002420.34mvemnzrwwsaesw@amd.com> Message-ID: Subject: Re: [PATCH RFC gmem v1 8/8] KVM: x86: Determine shared/private faults based on vm_type From: Sean Christopherson To: Michael Roth Cc: kvm@vger.kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-crypto@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, pbonzini@redhat.com, isaku.yamahata@intel.com, ackerleytng@google.com, vbabka@suse.cz, ashish.kalra@amd.com, nikunj.dadhania@amd.com, jroedel@suse.de, pankaj.gupta@amd.com, thomas.lendacky@amd.com Content-Type: text/plain; charset="us-ascii" On Wed, Feb 07, 2024, Michael Roth wrote: > On Tue, Jan 30, 2024 at 05:13:00PM -0800, Sean Christopherson wrote: > > On Mon, Oct 16, 2023, Michael Roth wrote: > > > For KVM_X86_SNP_VM, only the PFERR_GUEST_ENC_MASK flag is needed to > > > determine with an #NPF is due to a private/shared access by the guest. > > > Implement that handling here. Also add handling needed to deal with > > > SNP guests which in some cases will make MMIO accesses with the > > > encryption bit. > > > > ... > > > > > @@ -4356,12 +4357,19 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault > > > return RET_PF_EMULATE; > > > } > > > > > > - if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn)) { > > > + /* > > > + * In some cases SNP guests will make MMIO accesses with the encryption > > > + * bit set. Handle these via the normal MMIO fault path. > > > + */ > > > + if (!slot && private_fault && kvm_is_vm_type(vcpu->kvm, KVM_X86_SNP_VM)) > > > + private_fault = false; > > > > Why? This is inarguably a guest bug. > > AFAICT this isn't explicitly disallowed by the SNP spec. There are _lots_ of things that aren't explicitly disallowed by the APM, that doesn't mean that _KVM_ needs to actively support them. I am *not* taking on more broken crud in KVM to workaround OVMF's stupidity, the KVM_X86_QUIRK_CD_NW_CLEARED has taken up literally days of my time at this point. > So KVM would need to allow for these cases in order to be fully compatible > with existing SNP guests that do this. No. KVM does not yet support SNP, so as far as KVM's ABI goes, there are no existing guests. Yes, I realize that I am burying my head in the sand to some extent, but it is simply not sustainable for KVM to keep trying to pick up the pieces of poorly defined hardware specs and broken guest firmware. > > > +static bool kvm_mmu_fault_is_private(struct kvm *kvm, gpa_t gpa, u64 err) > > > +{ > > > + bool private_fault = false; > > > + > > > + if (kvm_is_vm_type(kvm, KVM_X86_SNP_VM)) { > > > + private_fault = !!(err & PFERR_GUEST_ENC_MASK); > > > + } else if (kvm_is_vm_type(kvm, KVM_X86_SW_PROTECTED_VM)) { > > > + /* > > > + * This handling is for gmem self-tests and guests that treat > > > + * userspace as the authority on whether a fault should be > > > + * private or not. > > > + */ > > > + private_fault = kvm_mem_is_private(kvm, gpa >> PAGE_SHIFT); > > > + } > > > > This can be more simply: > > > > if (kvm_is_vm_type(kvm, KVM_X86_SNP_VM)) > > return !!(err & PFERR_GUEST_ENC_MASK); > > > > if (kvm_is_vm_type(kvm, KVM_X86_SW_PROTECTED_VM)) > > return kvm_mem_is_private(kvm, gpa >> PAGE_SHIFT); > > > > Yes, indeed. But TDX has taken a different approach for SW_PROTECTED_VM > case where they do this check in kvm_mmu_page_fault() and then synthesize > the PFERR_GUEST_ENC_MASK into error_code before calling > kvm_mmu_do_page_fault(). It's not in the v18 patchset AFAICT, but it's > in the tdx-upstream git branch that corresponds to it: > > https://github.com/intel/tdx/commit/3717a903ef453aa7b62e7eb65f230566b7f158d4 > > Would you prefer that SNP adopt the same approach? Ah, yes, 'twas my suggestion in the first place. FWIW, I was just reviewing the literal code here and wasn't paying much attention to the content. https://lore.kernel.org/all/f474282d701aca7af00e4f7171445abb5e734c6f.1689893403.git.isaku.yamahata@intel.com