The HCR.TID3 bit defines that we should trap to the hypervisor for
reads to a collection of ID registers. Different architecture versions
have defined this differently:
* v7A has a set of ID regs that definitely must trap:
- ID_PFR{0,1}, ID_DFR0, ID_AFR0, ID_MMFR{0,1,2,3},
ID_ISAR{0,1,2,3,4,5}, MVFR{0,1}
and somewhat vaguely says that "there is no requirement"
to trap for registers that are reserved in the ID reg space
(i.e. which RAZ and might be used for new ID regs in future)
* v8A adds to this list:
- ID_PFR2 and MVFR2 must trap
- ID_MMFR4, ID_MMFR5, ID_ISAR6, ID_DFR1 and reserved registers
in the ID reg space must trap if FEAT_FGT is implemented,
and it is IMPDEF if they trap if FEAT_FGT is not implemented
In QEMU we seem to have attempted to implement this distinction
(taking the "we do trap" IMPDEF choice if no FEAT_FGT), with
access_aa64_tid3() always trapping on TID3 and access_aa32_tid3()
trapping only if ARM_FEATURE_V8 is set. However, we didn't apply
these to the right set of registers: we use access_aa32_tid3() on all
the 32-bit ID registers *except* ID_PFR2, ID_DFR1, ID_MMFR5 and the
RES0 space, which means that for a v7 CPU we don't trap on a lot of
registers that we should trap on, and we do trap on various things
that the v7A Arm ARM says there is "no requirement" to trap on.
Straighten this out by naming the access functions more clearly for
their purpose, and documenting this: access_v7_tid3() is only for the
fixed set of ID registers that v7A traps on HCR.TID3, and
access_tid3() is for any others, including the reserved encoding
spaces and any new registers we add in future.
AArch32 MVFR2 access is handled differently, in check_hcr_el2_trap;
there we already do not trap on TID3 on v7A cores (where MVFR2
doesn't exist), because we in the code-generation function we UNDEF
if ARM_FEATURE_V8 is not set, without generating code to call
check_hcr_el2_trap.
This bug was causing a problem for Xen which (after a recent change
to Xen) expects to be able to trap ID_PFR0 on a Cortex-A15.
The result of these changes is that our v8A behaviour remains
the same, and on v7A we now trap the registers the Arm ARM definitely
requires us to trap, and don't trap the reserved space that "there is
no requirement" to trap.
Cc: qemu-stable@nongnu.org
Fixes: 6a4ef4e5d1 ("target/arm: Honor HCR_EL2.TID3 trapping requirements")
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20251231170858.254594-3-peter.maydell@linaro.org
(cherry picked from commit 205ca535abaceda375c54797b1129a54a5ebbe96)
(Mjt: trivial context fix around AA64MMFR4_EL1 definition)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
5ead00ce11