The icount-based QEMU_CLOCK_VIRTUAL runs ahead of the RT clock at times.
When warping, it is possible it is still ahead at the end of the warp,
which causes icount adaptive mode to adjust it backward. This can result
in the machine observing time going backwards.

Prevent this by clamping adaptive adjustment to 0 at minimum.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Message-ID: <20230627061406.241847-1-npiggin@gmail.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

On Intel CPUs there are certain bits in MSR_ARCH_CAPABILITIES that
indicates if the CPU is not affected by a vulnerability. Without these
bits guests may try to deploy the mitigation even if the CPU is not
affected.

Export the bits to guests that indicate immunity to hardware
vulnerabilities.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Message-ID: <63d85cc76d4cdc51e6c732478b81d8f13be11e5a.1687551881.git.pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

ARCH_CAPABILITIES is only accessible through a read-only MSR, so it has
no impact on any user-mode operation (user-mode cannot read the MSR).
So do not bother printing warnings about it in user mode emulation.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Features such as PCID are only accessible through privileged operations,
and therefore have no impact on any user-mode operation.  Allow reporting
them to programs running under user mode emulation, so that "-cpu" can be
used with more named CPU models.

XSAVES would be similar, but it doesn't make sense to provide it until
XSAVEC is implemented.

With this change, all CPUs up to Broadwell-v4 can be emulate.  Skylake-Client
requires XSAVEC, while EPYC also requires SHA-NI, MISALIGNSSE and TOPOEXT.
MISALIGNSSE is not hard to implement, but I am not sure it is worth using
a precious hflags bit for it.

Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1534
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

32-bit binaries can run on a long mode processor even if the kernel
is 64-bit, of course, and this can have slightly different behavior;
for example, SYSCALL is allowed on Intel processors.

Allow reporting LM to programs running under user mode emulation,
so that "-cpu" can be used with named CPU models even for qemu-i386
and even without disabling LM by hand.

Fortunately, most of the runtime code in QEMU has to depend on HF_LMA_MASK
or on HF_CS64_MASK (which is anyway false for qemu-i386's 32-bit code
segment) rather than TARGET_X86_64, therefore all that is needed is an
update of linux-user's ring 0 setup.

Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1534
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

* Make named CPU models usable for qemu-{i386,x86_64}
* Fix backwards time with -icount auto

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# gpg: Signature made Thu 29 Jun 2023 10:51:48 AM CEST
# gpg:                using RSA key F13338574B662389866C7682BFFBD25F78C7AE83
# gpg:                issuer "pbonzini@redhat.com"
# gpg: Good signature from "Paolo Bonzini <bonzini@gnu.org>" [undefined]
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* tag 'for-upstream' of https://gitlab.com/bonzini/qemu:
  target/i386: emulate 64-bit ring 0 for linux-user if LM feature is set
  target/i386: ignore CPL0-specific features in user mode emulation
  target/i386: ignore ARCH_CAPABILITIES features in user mode emulation
  target/i386: Export MSR_ARCH_CAPABILITIES bits to guests
  icount: don't adjust virtual time backwards after warp

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>