From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Michal Luczaj <mhal@rbox.co>,
David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH v2 03/16] KVM: x86: Always use non-compat vcpu_runstate_info size for gfn=>pfn cache
Date: Thu, 27 Oct 2022 15:10:07 +0000 [thread overview]
Message-ID: <Y1qfT2Mnwk5GmjFI@google.com> (raw)
In-Reply-To: <24768aa3-0e2e-6d29-2749-9d74a26f9205@redhat.com>
On Thu, Oct 27, 2022, Paolo Bonzini wrote:
> On 10/27/22 16:44, Sean Christopherson wrote:
> > > - long mode cannot be changed after the shared info page is enabled (which
> > > makes sense because the shared info page also has a compat version)
> >
> > How is this not introducing an additional restriction? This seems way more
> > onerous than what is effectively a revert.
> >
> > > - the caches must be activated after the shared info page (which enforces
> > > that the vCPU attributes are set after the VM attributes)
> > >
> > > This is technically a userspace API break, but nobody is really using this
> > > API outside Amazon so... Patches coming after I finish testing.
> >
> > It's not just userspace break, it affects the guest ABI as well.
>
> Yes, I was talking of the VMM here; additional restrictions are fine there.
Additional restrictions are fine where?
> The guests however should be compatible with Xen, so you also need to
> re-activate the cache after the hypercall page is written, but that's two
> lines of code.
And do what if the guest transitions from 32-bit => 64-bit and the cache isn't
aligned for 64-bit? E.g. kvm_xen_set_evtchn() will silently drop events no matter
what KVM does. In other words, I don't see how KVM can provide a same ABI without
forcing the cached pages to be aligned for the largets possible size.
next prev parent reply other threads:[~2022-10-27 15:13 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-13 21:12 [PATCH v2 00/16] KVM: x86: gfn_to_pfn_cache fixes and cleanups Sean Christopherson
2022-10-13 21:12 ` [PATCH v2 01/16] KVM: Initialize gfn_to_pfn_cache locks in dedicated helper Sean Christopherson
2022-10-13 21:12 ` [PATCH v2 02/16] KVM: Reject attempts to consume or refresh inactive gfn_to_pfn_cache Sean Christopherson
2022-10-13 21:12 ` [PATCH v2 03/16] KVM: x86: Always use non-compat vcpu_runstate_info size for gfn=>pfn cache Sean Christopherson
2022-10-27 11:11 ` Paolo Bonzini
2022-10-27 14:44 ` Sean Christopherson
2022-10-27 15:03 ` Paolo Bonzini
2022-10-27 15:10 ` Sean Christopherson [this message]
2022-10-27 16:56 ` Sean Christopherson
2022-10-13 21:12 ` [PATCH v2 04/16] KVM: Shorten gfn_to_pfn_cache function names Sean Christopherson
2022-10-13 21:12 ` [PATCH v2 05/16] KVM: x86: Remove unused argument in gpc_unmap_khva() Sean Christopherson
2022-12-02 9:28 ` Like Xu
2022-12-02 10:57 ` Michal Luczaj
2022-12-02 14:21 ` David Woodhouse
2022-12-02 17:01 ` Sean Christopherson
2022-10-13 21:12 ` [PATCH v2 06/16] KVM: Store immutable gfn_to_pfn_cache properties Sean Christopherson
2022-10-13 21:12 ` [PATCH v2 07/16] KVM: Store gfn_to_pfn_cache length as an immutable property Sean Christopherson
2022-11-21 14:26 ` David Woodhouse
2022-11-21 19:11 ` Sean Christopherson
2022-11-21 20:02 ` David Woodhouse
2022-11-22 18:59 ` Sean Christopherson
2022-10-13 21:12 ` [PATCH v2 08/16] KVM: Use gfn_to_pfn_cache's immutable "kvm" in kvm_gpc_check() Sean Christopherson
2022-10-13 21:12 ` [PATCH v2 09/16] KVM: Clean up hva_to_pfn_retry() Sean Christopherson
2022-10-13 21:12 ` [PATCH v2 10/16] KVM: Use gfn_to_pfn_cache's immutable "kvm" in kvm_gpc_refresh() Sean Christopherson
2022-10-13 21:12 ` [PATCH v2 11/16] KVM: Drop KVM's API to allow temprorarily unmapping gfn=>pfn cache Sean Christopherson
2022-10-13 21:12 ` [PATCH v2 12/16] KVM: Do not partially reinitialize gfn=>pfn cache during activation Sean Christopherson
2022-10-13 21:12 ` [PATCH v2 13/16] KVM: Drop @gpa from exported gfn=>pfn cache check() and refresh() helpers Sean Christopherson
2022-10-13 21:12 ` [PATCH v2 14/16] KVM: Skip unnecessary "unmap" if gpc is already valid during refresh Sean Christopherson
2022-10-13 21:12 ` [PATCH v2 15/16] KVM: selftests: Add tests in xen_shinfo_test to detect lock races Sean Christopherson
2022-10-13 21:12 ` [PATCH v2 16/16] KVM: selftests: Mark "guest_saw_irq" as volatile in xen_shinfo_test Sean Christopherson
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