KVM: nVMX: Do not clear CR3 load/store exiting bits if L1 wants 'em

stable inclusion
from stable-v5.10.190
commit c710ff061237f10269eb18c4a8f435a64138b26a
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I928UI

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c710ff061237f10269eb18c4a8f435a64138b26a



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[ Upstream commit 470750b3 ]

Keep CR3 load/store exiting enable as needed when running L2 in order to
honor L1's desires.  This fixes a largely theoretical bug where L1 could
intercept CR3 but not CR0.PG and end up not getting the desired CR3 exits
when L2 enables paging.  In other words, the existing !is_paging() check
inadvertantly handles the normal case for L2 where vmx_set_cr0() is
called during VM-Enter, which is guaranteed to run with paging enabled,
and thus will never clear the bits.

Removing the !is_paging() check will also allow future consolidation and
cleanup of the related code.  From a performance perspective, this is
all a nop, as the VMCS controls shadow will optimize away the VMWRITE
when the controls are in the desired state.

Add a comment explaining why CR3 is intercepted, with a big disclaimer
about not querying the old CR3.  Because vmx_set_cr0() is used for flows
that are not directly tied to MOV CR3, e.g. vCPU RESET/INIT and nested
VM-Enter, it's possible that is_paging() is not synchronized with CR3
load/store exiting.  This is actually guaranteed in the current code, as
KVM starts with CR3 interception disabled.  Obviously that can be fixed,
but there's no good reason to play whack-a-mole, and it tends to end
poorly, e.g. descriptor table exiting for UMIP emulation attempted to be
precise in the past and ended up botching the interception toggling.

Fixes: fe3ef05c ("KVM: nVMX: Prepare vmcs02 from vmcs01 and vmcs12")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-25-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Stable-dep-of: c4abd735 ("KVM: VMX: Don't fudge CR0 and CR4 for restricted L2 guest")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>