From: Sean Christopherson <seanjc@google.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>
Subject: Re: [PATCH RFC 3/4] KVM: Define KVM_USER_MEM_SLOTS in arch-neutral include/linux/kvm_host.h
Date: Fri, 15 Jan 2021 09:05:09 -0800 [thread overview]
Message-ID: <YAHLRVhevn7adhAz@google.com> (raw)
In-Reply-To: <20210115131844.468982-4-vkuznets@redhat.com>
On Fri, Jan 15, 2021, Vitaly Kuznetsov wrote:
> Memory slots are allocated dynamically when added so the only real
> limitation in KVM is 'id_to_index' array which is 'short'. Define
> KVM_USER_MEM_SLOTS to the maximum possible value in the arch-neutral
> include/linux/kvm_host.h, architectures can still overtide the setting
> if needed.
Leaving the max number of slots nearly unbounded is probably a bad idea. If my
math is not completely wrong, this would let userspace allocate 6mb of kernel
memory per VM. Actually, worst case scenario would be 12mb since modifying
memslots temporarily has two allocations.
If we remove the arbitrary limit, maybe replace it with a module param with a
sane default?
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> include/linux/kvm_host.h | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index f3b1013fb22c..ab83a20a52ca 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -425,6 +425,10 @@ struct kvm_irq_routing_table {
> #define KVM_PRIVATE_MEM_SLOTS 0
> #endif
>
> +#ifndef KVM_USER_MEM_SLOTS
> +#define KVM_USER_MEM_SLOTS (SHRT_MAX - KVM_PRIVATE_MEM_SLOTS)
> +#endif
> +
> #ifndef KVM_MEM_SLOTS_NUM
> #define KVM_MEM_SLOTS_NUM (KVM_USER_MEM_SLOTS + KVM_PRIVATE_MEM_SLOTS)
> #endif
> --
> 2.29.2
>
next prev parent reply other threads:[~2021-01-15 17:06 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-15 13:18 [PATCH RFC 0/4] KVM: x86: Drastically raise KVM_USER_MEM_SLOTS limit Vitaly Kuznetsov
2021-01-15 13:18 ` [PATCH RFC 1/4] KVM: x86: Drop redundant KVM_MEM_SLOTS_NUM definition Vitaly Kuznetsov
2021-01-15 16:47 ` Sean Christopherson
2021-01-15 13:18 ` [PATCH RFC 2/4] KVM: mips: Drop KVM_PRIVATE_MEM_SLOTS definition Vitaly Kuznetsov
2021-01-15 13:18 ` [PATCH RFC 3/4] KVM: Define KVM_USER_MEM_SLOTS in arch-neutral include/linux/kvm_host.h Vitaly Kuznetsov
2021-01-15 17:05 ` Sean Christopherson [this message]
2021-01-18 9:52 ` Vitaly Kuznetsov
2021-01-19 17:20 ` Sean Christopherson
2021-01-20 11:34 ` Igor Mammedov
2021-01-20 12:02 ` Vitaly Kuznetsov
2021-01-20 17:25 ` Sean Christopherson
2021-01-15 13:18 ` [PATCH RFC 4/4] KVM: x86: Stop limiting KVM_USER_MEM_SLOTS Vitaly Kuznetsov
2021-01-15 16:03 ` [PATCH RFC 0/4] KVM: x86: Drastically raise KVM_USER_MEM_SLOTS limit Sean Christopherson
2021-01-15 16:23 ` Vitaly Kuznetsov
2021-01-15 16:45 ` Sean Christopherson
2021-01-15 18:47 ` Maciej S. Szmigiero
2021-01-27 17:55 ` Vitaly Kuznetsov
2021-01-27 22:26 ` Maciej S. Szmigiero
2021-01-28 8:47 ` Vitaly Kuznetsov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YAHLRVhevn7adhAz@google.com \
--to=seanjc@google.com \
--cc=jmattson@google.com \
--cc=kvm@vger.kernel.org \
--cc=pbonzini@redhat.com \
--cc=vkuznets@redhat.com \
--cc=wanpengli@tencent.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).