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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.googlemail.com with ESMTPSA id h9-20020adff189000000b001ea913352c9sm14590055wro.100.2022.03.01.12.17.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 01 Mar 2022 12:17:55 -0800 (PST) Message-ID: Date: Tue, 1 Mar 2022 21:17:53 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH AUTOSEL 5.15 06/23] kvm: x86: Disable KVM_HC_CLOCK_PAIRING if tsc is in always catchup mode Content-Language: en-US To: Sasha Levin , linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Anton Romanov , tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, kvm@vger.kernel.org References: <20220301201629.18547-1-sashal@kernel.org> <20220301201629.18547-6-sashal@kernel.org> From: Paolo Bonzini In-Reply-To: <20220301201629.18547-6-sashal@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/1/22 21:16, Sasha Levin wrote: > From: Anton Romanov > > [ Upstream commit 3a55f729240a686aa8af00af436306c0cd532522 ] > > If vcpu has tsc_always_catchup set each request updates pvclock data. > KVM_HC_CLOCK_PAIRING consumers such as ptp_kvm_x86 rely on tsc read on > host's side and do hypercall inside pvclock_read_retry loop leading to > infinite loop in such situation. > > v3: > Removed warn > Changed return code to KVM_EFAULT > v2: > Added warn > > Signed-off-by: Anton Romanov > Message-Id: <20220216182653.506850-1-romanton@google.com> > Signed-off-by: Paolo Bonzini > Signed-off-by: Sasha Levin > --- > arch/x86/kvm/x86.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 33cb065181248..c804122bb6e3a 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -8657,6 +8657,13 @@ static int kvm_pv_clock_pairing(struct kvm_vcpu *vcpu, gpa_t paddr, > if (clock_type != KVM_CLOCK_PAIRING_WALLCLOCK) > return -KVM_EOPNOTSUPP; > > + /* > + * When tsc is in permanent catchup mode guests won't be able to use > + * pvclock_read_retry loop to get consistent view of pvclock > + */ > + if (vcpu->arch.tsc_always_catchup) > + return -KVM_EOPNOTSUPP; > + > if (!kvm_get_walltime_and_clockread(&ts, &cycle)) > return -KVM_EOPNOTSUPP; > Acked-by: Paolo Bonzini