Re: [PATCH v4 10/10] arm64: ptdump: Add guest stage-2 pagetables dumping

From: Oliver Upton <oliver.upton@linux.dev>
To: Sebastian Ene <sebastianene@google.com>
Cc: will@kernel.org, James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	catalin.marinas@arm.com, mark.rutland@arm.com,
	akpm@linux-foundation.org, maz@kernel.org,
	kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, kernel-team@android.com,
	vdonnefort@google.com, qperret@google.com, smostafa@google.com
Subject: Re: [PATCH v4 10/10] arm64: ptdump: Add guest stage-2 pagetables dumping
Date: Thu, 21 Dec 2023 18:27:59 +0000	[thread overview]
Message-ID: <ZYSDr9uYi3cUk_Jt@linux.dev> (raw)
In-Reply-To: <20231218135859.2513568-12-sebastianene@google.com>

On Mon, Dec 18, 2023 at 01:59:00PM +0000, Sebastian Ene wrote:
> Register a debugfs file on guest creation to be able to view their
> second translation tables with ptdump. This assumes that the host is in
> control of the guest stage-2 and has direct access to the pagetables.
> 
> Signed-off-by: Sebastian Ene <sebastianene@google.com>

I couldn't see how this patched worked at all until I went back to patch
1 and found this:

> +static int kvm_ptdump_open(struct inode *inode, struct file *file)
> +{

[...]

> +	if (!reg->show_ptdump_info)
> +		reg->show_ptdump_info = kvm_ptdump_show;

[...]

> +}

> +static int kvm_ptdump_show(struct seq_file *m, void *)
> +{
> +	struct kvm *guest_kvm = m->private;
> +	struct kvm_s2_mmu *mmu = &guest_kvm->arch.mmu;
> +	int ret;
> +
> +	write_lock(&guest_kvm->mmu_lock);
> +	ret = kvm_ptdump_show_common(m, mmu->pgt);
> +	write_unlock(&guest_kvm->mmu_lock);
> +
> +	return ret;
> +}

Where are you getting a reference on the kvm struct? You need to do this
to ensure the VM doesn't get destroyed behind your back.

-- 
Thanks,
Oliver