From: Sean Christopherson <seanjc@google.com>
To: "Woodhouse, David" <dwmw@amazon.co.uk>
Cc: "pbonzini@redhat.com" <pbonzini@redhat.com>,
"mhal@rbox.co" <mhal@rbox.co>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"Durrant, Paul" <pdurrant@amazon.co.uk>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Kaya, Metin" <metikaya@amazon.co.uk>
Subject: Re: [PATCH 03/16] KVM: x86: set gfn-to-pfn cache length consistently with VM word size
Date: Mon, 14 Nov 2022 16:33:27 +0000 [thread overview]
Message-ID: <Y3Jt11kcj8lQ+NCN@google.com> (raw)
In-Reply-To: <994314051112513787cc4bd0c7d2694e15190d0f.camel@amazon.co.uk>
On Mon, Nov 14, 2022, Woodhouse, David wrote:
> Most other data structures, including the pvclock info (both Xen and
> native KVM), could potentially cross page boundaries. And isn't that
> also true for things that we'd want to use the GPC for in nesting?
Off the top of my head, no. Except for MSR and I/O permission bitmaps, which
are >4KiB, things that are referenced by physical address are <=4KiB and must be
naturally aligned. nVMX does temporarily map L1's MSR bitmap, but that could be
split into two separate mappings if necessary.
> For the runstate info I suggested reverting commit a795cd43c5b5 but
> that doesn't actually work because it still has the same problem. Even
> the gfn-to-hva cache still only really works for a single page, and
> things like kvm_write_guest_offset_cached() will fall back to using
> kvm_write_guest() in the case where it crosses a page boundary.
>
> I'm wondering if the better fix is to allow the GPC to map more than
> one page.
I agree that KVM should drop the "no page splits" restriction, but I don't think
that would necessarily solve all KVM Xen issues. KVM still needs to precisely
handle the "correct" struct size, e.g. if one of the structs is placed at the very
end of the page such that the smaller compat version doesn't split a page but the
64-bit version does.
next prev parent reply other threads:[~2022-11-14 16:38 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-27 16:18 [PATCH v3 00/16] KVM: x86: Always use non-compat vcpu_runstate_info size for gfn=>pfn cache Paolo Bonzini
2022-10-27 16:18 ` [PATCH 01/16] KVM: Initialize gfn_to_pfn_cache locks in dedicated helper Paolo Bonzini
2022-10-27 16:18 ` [PATCH 02/16] KVM: Reject attempts to consume or refresh inactive gfn_to_pfn_cache Paolo Bonzini
2022-10-27 16:18 ` [PATCH 03/16] KVM: x86: set gfn-to-pfn cache length consistently with VM word size Paolo Bonzini
2022-10-27 17:22 ` Sean Christopherson
2022-10-28 11:36 ` Paolo Bonzini
2022-10-28 16:31 ` Sean Christopherson
2022-11-13 13:32 ` David Woodhouse
2022-11-13 13:36 ` David Woodhouse
2022-11-14 11:27 ` Durrant, Paul
2022-11-15 0:16 ` David Woodhouse
2022-11-16 22:49 ` David Woodhouse
[not found] ` <994314051112513787cc4bd0c7d2694e15190d0f.camel@amazon.co.uk>
2022-11-14 16:33 ` Sean Christopherson [this message]
2022-11-14 17:36 ` [EXTERNAL][PATCH " David Woodhouse
2022-11-14 16:58 ` [PATCH " Paolo Bonzini
2022-10-27 16:18 ` [PATCH 04/16] KVM: Shorten gfn_to_pfn_cache function names Paolo Bonzini
2022-10-27 16:18 ` [PATCH 05/16] KVM: x86: Remove unused argument in gpc_unmap_khva() Paolo Bonzini
2022-10-27 16:18 ` [PATCH 06/16] KVM: Store immutable gfn_to_pfn_cache properties Paolo Bonzini
2022-10-27 16:18 ` [PATCH 07/16] KVM: Store gfn_to_pfn_cache length at activation time Paolo Bonzini
2022-10-27 16:18 ` [PATCH 08/16] KVM: Use gfn_to_pfn_cache's immutable "kvm" in kvm_gpc_check() Paolo Bonzini
2022-10-27 16:18 ` [PATCH 09/16] KVM: Clean up hva_to_pfn_retry() Paolo Bonzini
2022-10-27 16:18 ` [PATCH 10/16] KVM: Use gfn_to_pfn_cache's immutable "kvm" in kvm_gpc_refresh() Paolo Bonzini
2022-10-27 16:18 ` [PATCH 11/16] KVM: Drop KVM's API to allow temprorarily unmapping gfn=>pfn cache Paolo Bonzini
2022-10-27 16:18 ` [PATCH 12/16] KVM: Do not partially reinitialize gfn=>pfn cache during activation Paolo Bonzini
2022-10-27 16:18 ` [PATCH 13/16] KVM: Drop @gpa from exported gfn=>pfn cache check() and refresh() helpers Paolo Bonzini
2022-10-27 16:18 ` [PATCH 14/16] KVM: Skip unnecessary "unmap" if gpc is already valid during refresh Paolo Bonzini
2022-10-27 16:18 ` [PATCH 15/16] KVM: selftests: Add tests in xen_shinfo_test to detect lock races Paolo Bonzini
2022-10-27 16:18 ` [PATCH 16/16] KVM: selftests: Mark "guest_saw_irq" as volatile in xen_shinfo_test Paolo Bonzini
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