From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.com>,
Colin King <colin.king@canonical.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
David Stevens <stevensd@chromium.org>,
kvm@vger.kernel.org, kernel-janitors@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH][next] KVM: x86: Fix allocation sizeof argument
Date: Tue, 5 Oct 2021 19:27:31 +0200 [thread overview]
Message-ID: <ebd506ba-05cc-99d7-ece5-34bd67fc2430@redhat.com> (raw)
In-Reply-To: <YVxyNgyyxA7EnvJb@google.com>
On 05/10/21 17:41, Sean Christopherson wrote:
>> if (*gfn_track == NULL) {
>> mutex_unlock(&kvm->slots_arch_lock);
> Hrm, this fails to free the gfn_track allocations for previous memslots. The
> on-demand rmaps code has the exact same bug (it frees rmaps for previous lpages
> in the_current_ slot, but does not free previous slots).
That's not a huge deal because the syscall is failing. So as long as
it's not leaked forever, it's okay. The problem is the
WARN_ON(slot->arch.rmap[i]), or the missing check in
kvm_page_track_enable_mmu_write_tracking, but that's easily fixed. I'd
even remove the call to memslot_rmaps_free.
> And having two separate flows (and flags) for rmaps vs. gfn_track is pointless,
> and means we have to maintain two near-identical copies of non-obvious code.
I was thinking the separate flow (not so much the flag) is needed
because, if KVMGT is enabled, gfn_track is allocated unconditionally.
rmaps are added on top of that if shadow paging is enabled; but
kvm_page_track_create_memslot will have already created the counter,
including the one for KVM_PAGE_TRACK_WRITE.
But looking at the code again, I guess you could call
kvm_page_track_enable_mmu_write_tracking inside alloc_all_memslots_rmaps
(with a little bit of renaming), and with that the flag would go away.
I'll take a look tomorrow, but I'd rather avoid reverting the patch.
Thanks,
Paolo
> Paolo, is it too late to just drop the original deae4a10f166 ("KVM: x86: only
> allocate gfn_track when necessary")?
>
next prev parent reply other threads:[~2021-10-05 17:27 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-01 11:01 [PATCH][next] KVM: x86: Fix allocation sizeof argument Colin King
2021-10-05 15:41 ` Sean Christopherson
2021-10-05 17:27 ` Paolo Bonzini [this message]
2021-10-05 17:55 ` Sean Christopherson
2021-10-05 20:52 ` Paolo Bonzini
2021-10-06 0:22 ` David Stevens
2021-10-06 0:41 ` Sean Christopherson
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