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[2003:f6:af1b:ce00:e6fe:5f11:c0a7:f4a1]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-441b89ee39esm133833415e9.21.2025.05.05.07.01.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 05 May 2025 07:01:25 -0700 (PDT) Date: Mon, 5 May 2025 16:01:24 +0200 (CEST) From: Sebastian Ott To: Marc Zyngier cc: Oliver Upton , Quentin Perret , Fuad Tabba , Catalin Marinas , Will Deacon , Mark Brown , Mark Rutland , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: LM regression: fce886a60207 KVM: arm64: Plumb the pKVM MMU in KVM In-Reply-To: <86msbrguka.wl-maz@kernel.org> Message-ID: References: <3f5db4c7-ccce-fb95-595c-692fa7aad227@redhat.com> <86msbrguka.wl-maz@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed On Mon, 5 May 2025, Marc Zyngier wrote: > On Mon, 05 May 2025 11:52:00 +0100, > Sebastian Ott wrote: >> Doing back and forth migrations currently fails on arm after a couple iterations. >> During the failing migration KVM_RUN exits via guest_abort and returns -ENOMEM. >> I can reliably reproduce this by migrating between 2 qemu instances on an ampere >> altra machine. This fails after < 5 iterations. In this case qemu would spit out >> smth like this (other than that - nothing in the logs): >> >> error: kvm run failed Cannot allocate memory >> PC=0000aaaae7d48590 X00=0000aaaae80a2e00 X01=0000aaaae7ea2fc0 >> X02=0000000001d3a5d0 X03=0000aaaae7eace8c X04=000000003b9aca00 >> X05=000000000000004a X06=000000000000004a X07=0000000028000000 >> X08=0000000000001d70 X09=0000000000000018 X10=000144b7d0000000 >> X11=00ffffffffffffff X12=000000008378f367 X13=0000aaab1a202d70 >> X14=0000000000000000 X15=0000000000000000 X16=0000ffffa2e2f7a8 >> X17=0000ffffa2541f20 X18=000000000000a000 X19=84bfda6288cf2dd6 >> X20=0000aaab1a1f1ce0 X21=000000007fffffff X22=0000ffffc5431788 >> X23=0000aaab1a17db60 X24=0000ffffc5431770 X25=0000000100000000 >> X26=0000004100000000 X27=0000000000000001 X28=0000aaab1a1f1c20 >> X29=0000ffffc54316d0 X30=0000aaaae7f8cd24 SP=0000ffffc5431650 >> PSTATE=20001000 --C- EL0t >> >> Guest and host are otherwise idle, kvm is in normal VHE mode. >> >> Git bisect points to (fce886a60207 "KVM: arm64: Plumb the pKVM MMU in KVM") >> I also double checked that by reverting this commit on top of 6.14. > > Thanks for find the triggering commit. Can you further identify *what* > causes the -ENOMEM? The only new -ENOMEM in that patch is the one > added to topup_hyp_memcache(), which shouldn't be called. The kvm_pgtable_stage2_map() call in user_mem_abort() returns -ENOMEM because the memcache pointer was not initialized! It looks like smth like this without other conditions could do the trick: if (!is_protected_kvm_enabled()) memcache = &vcpu->arch.mmu_page_cache; else memcache = &vcpu->arch.pkvm_memcache; (I'll try this now) > Also, a failure to allocate would leave some nastygram in the kernel > log, so it is unlikely to be an actual failure to allocate. > > Is it the first KVM_RUN that fails after migration? Nope, it happens on the side that triggers the migration. Sebastian