linux-kernel - Re: [PATCH 2/3] KVM: x86: Add support for VMware guest specific hypercalls

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <93df442c-8ec3-43ee-aba1-e770a5b7588f@redhat.com>
Date: Mon, 3 Feb 2025 20:46:32 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>,
 Doug Covelli <doug.covelli@...adcom.com>
Cc: Zack Rusin <zack.rusin@...adcom.com>, kvm <kvm@...r.kernel.org>,
 Jonathan Corbet <corbet@....net>, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 the arch/x86 maintainers <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
 Shuah Khan <shuah@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
 Arnaldo Carvalho de Melo <acme@...hat.com>,
 Isaku Yamahata <isaku.yamahata@...el.com>, Joel Stanley <joel@....id.au>,
 Linux Doc Mailing List <linux-doc@...r.kernel.org>,
 linux-kernel@...r.kernel.org,
 linux-kselftest <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH 2/3] KVM: x86: Add support for VMware guest specific
 hypercalls

On 2/3/25 20:41, Sean Christopherson wrote:
> -EFAULT isn't the problem, KVM not being able to return useful information in
> all situations is the issue. 

Yes, that's why I don't want it to be an automatically opted-in API.  If 
incremental improvements are possible, it may be useful to allow 
interested userspace to enable it early.  For example...

> Specifically, "guest" accesses that are emulated
> by KVM are problematic, because the -EFAULT from e.g. __kvm_write_guest_page()
> is disconnected from the code that actually kicks out to userspace.  In that
> case, userspace will get KVM_EXIT_MMIO, not -EFAULT.  There are more problems
> beyond KVM_EXIT_MMIO vs. -EFAULT, e.g. instructions that perform multiple memory
> accesses,

those are obviously synchronous and I expect VMware to handle them already.

That said my preferred solution to just use userfaultfd, which is 
synchronous by definition.

Paolo

> "failures" that are squashed and never propagated to userspace (PV
> features tend to do this), page splits, etc.