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From: Oliver Upton <oliver.upton@linux.dev>
To: Fuad Tabba <tabba@google.com>
Cc: kvmarm@lists.linux.dev, maz@kernel.org, will@kernel.org,
	qperret@google.com, seanjc@google.com, alexandru.elisei@arm.com,
	catalin.marinas@arm.com, philmd@linaro.org, james.morse@arm.com,
	suzuki.poulose@arm.com, mark.rutland@arm.com, broonie@kernel.org,
	joey.gouly@arm.com, rananta@google.com, smostafa@google.com
Subject: Re: [PATCH v3 27/31] KVM: arm64: Use atomic refcount helpers for 'struct hyp_page::refcount'
Date: Mon, 22 Apr 2024 13:46:14 -0700	[thread overview]
Message-ID: <ZibMlkG-1MnCiXXF@linux.dev> (raw)
In-Reply-To: <CA+EHjTzc6h719kvP9FJA3xqLnOxr5gPWDq7iYOx7JfQz4Wn61w@mail.gmail.com>

On Mon, Apr 22, 2024 at 02:08:17PM +0100, Fuad Tabba wrote:

[...]

> > > Adding a BUG_ON() for taking a reference on a non-refcounted page (i.e.
> > > p->refcount was 0) would be nice, especially since we're past the point of
> > > serializing everything and you can theoretically have a zero count page
> > > outside of the free list.
> > >
> > > Seems like otherwise we'd get actually hit the BUG_ON() in an unrelated
> > > allocation path.
> 
> Actually, the refcount can be 0 without it being an error. For
> example, when hyp pins memory shared with it by the host
> (mem_protect.c:hyp_pin_shared_mem()).

Are those not by their very definition non-refcounted pages? I can't
imagine we'd want pages in a shared state with the host to ever get
returned to the hyp allocator. Seems an erroneous hyp_put_page() would
get you there, though.

-- 
Thanks,
Oliver

  reply	other threads:[~2024-04-22 20:46 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-04-19  7:59 [PATCH v3 00/31] KVM: arm64: Preamble for pKVM Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 01/31] KVM: arm64: Initialize the kvm host data's fpsimd_state pointer in pKVM Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 02/31] KVM: arm64: Move guest_owns_fp_regs() to increase its scope Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 03/31] KVM: arm64: Refactor checks for FP state ownership Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 04/31] KVM: arm64: Do not re-initialize the KVM lock Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 05/31] KVM: arm64: Issue CMOs when tearing down guest s2 pages Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 06/31] KVM: arm64: Avoid BUG-ing from the host abort path Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 07/31] KVM: arm64: Check for PTE validity when checking for executable/cacheable Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 08/31] KVM: arm64: Avoid BBM when changing only s/w bits in Stage-2 PTE Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 09/31] KVM: arm64: Support TLB invalidation in guest context Fuad Tabba
2024-04-19 20:54   ` Oliver Upton
2024-04-22  8:11     ` Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 10/31] KVM: arm64: Do not map the host fpsimd state to hyp in pKVM Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 11/31] KVM: arm64: Remove locking from EL2 allocation fast-paths Fuad Tabba
2024-04-19 20:42   ` Oliver Upton
2024-04-22  8:09     ` Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 12/31] KVM: arm64: Prevent kmemleak from accessing .hyp.data Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 13/31] KVM: arm64: Fix comment for __pkvm_vcpu_init_traps() Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 14/31] KVM: arm64: Change kvm_handle_mmio_return() return polarity Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 15/31] KVM: arm64: Move setting the page as dirty out of the critical section Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 16/31] KVM: arm64: Simplify vgic-v3 hypercalls Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 17/31] KVM: arm64: Add is_pkvm_initialized() helper Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 18/31] KVM: arm64: Introduce and use predicates that check for protected VMs Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 19/31] KVM: arm64: Move pstate reset value definitions to kvm_arm.h Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 20/31] KVM: arm64: Clarify rationale for ZCR_EL1 value restored on guest exit Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 21/31] KVM: arm64: Refactor calculating SVE state size to use helpers Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 22/31] KVM: arm64: Move some kvm_psci functions to a shared header Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 23/31] KVM: arm64: Refactor reset_mpidr() to extract its computation Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 24/31] KVM: arm64: Refactor kvm_vcpu_enable_ptrauth() for hyp use Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 25/31] KVM: arm64: Introduce hyp_rwlock_t Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 26/31] KVM: arm64: Add atomics-based checking refcount implementation at EL2 Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 27/31] KVM: arm64: Use atomic refcount helpers for 'struct hyp_page::refcount' Fuad Tabba
2024-04-19 20:52   ` Oliver Upton
2024-04-22  8:10     ` Fuad Tabba
2024-04-22 13:08       ` Fuad Tabba
2024-04-22 20:46         ` Oliver Upton [this message]
2024-04-22 23:44           ` Will Deacon
2024-04-23  1:15             ` Oliver Upton
2024-04-19  7:59 ` [PATCH v3 28/31] KVM: arm64: Reformat/beautify PTP hypercall documentation Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 29/31] KVM: arm64: Rename firmware pseudo-register documentation file Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 30/31] KVM: arm64: Document the KVM/arm64-specific calls in hypercalls.rst Fuad Tabba
2024-04-19  7:59 ` [PATCH v3 31/31] KVM: arm64: Force injection of a data abort on NISV MMIO exit Fuad Tabba
2024-04-19 20:28   ` Oliver Upton
2024-04-22  8:07     ` Fuad Tabba

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