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([2001:b07:6468:f312:1cb4:2b36:6750:73ce]) by smtp.gmail.com with ESMTPSA id u16sm8073375wrq.17.2020.05.09.05.59.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 09 May 2020 05:59:19 -0700 (PDT) Subject: Re: [PATCH v2 2/3] KVM: x86: Move pkru save/restore to x86.c To: Jim Mattson , Babu Moger Cc: Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H . Peter Anvin" , Sean Christopherson , the arch/x86 maintainers , Vitaly Kuznetsov , Wanpeng Li , Joerg Roedel , Dave Hansen , Andy Lutomirski , Peter Zijlstra , mchehab+samsung@kernel.org, changbin.du@intel.com, Nadav Amit , Sebastian Andrzej Siewior , yang.shi@linux.alibaba.com, asteinhauser@google.com, anshuman.khandual@arm.com, Jan Kiszka , Andrew Morton , steven.price@arm.com, rppt@linux.vnet.ibm.com, peterx@redhat.com, Dan Williams , arjunroy@google.com, logang@deltatee.com, Thomas Hellstrom , Andrea Arcangeli , justin.he@arm.com, robin.murphy@arm.com, ira.weiny@intel.com, Kees Cook , Juergen Gross , Andrew Cooper , pawan.kumar.gupta@linux.intel.com, "Yu, Fenghua" , vineela.tummalapalli@intel.com, yamada.masahiro@socionext.com, sam@ravnborg.org, acme@redhat.com, linux-doc@vger.kernel.org, LKML , kvm list References: <158897190718.22378.3974700869904223395.stgit@naples-babu.amd.com> <158897219574.22378.9077333868984828038.stgit@naples-babu.amd.com> From: Paolo Bonzini Message-ID: <90657d4b-cb2b-0678-fd9c-a281bb85fadf@redhat.com> Date: Sat, 9 May 2020 14:59:17 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 09/05/20 00:09, Jim Mattson wrote: >> + if (static_cpu_has(X86_FEATURE_PKU) && >> + kvm_read_cr4_bits(vcpu, X86_CR4_PKE) && >> + vcpu->arch.pkru != vcpu->arch.host_pkru) >> + __write_pkru(vcpu->arch.pkru); > This doesn't seem quite right to me. Though rdpkru and wrpkru are > contingent upon CR4.PKE, the PKRU resource isn't. It can be read with > XSAVE and written with XRSTOR. So, if we don't set the guest PKRU > value here, the guest can read the host value, which seems dodgy at > best. > > Perhaps the second conjunct should be: (kvm_read_cr4_bits(vcpu, > X86_CR4_PKE) || (vcpu->arch.xcr0 & XFEATURE_MASK_PKRU)). You're right. The bug was preexistent, but we should fix it in 5.7 and stable as well. >> } >> EXPORT_SYMBOL_GPL(kvm_load_guest_xsave_state); >> >> void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu) >> { >> + /* >> + * eager fpu is enabled if PKEY is supported and CR4 is switched >> + * back on host, so it is safe to read guest PKRU from current >> + * XSAVE. >> + */ > I don't understand the relevance of this comment to the code below. > It's probably stale. Paolo