Re: [PATCH v3 5/6] target/arm: Do memory type alignment check when translation disabled

[Jonathan Cameron via <qemu-devel@nongnu.org>]

On Fri,  1 Mar 2024 10:41:09 -1000
Richard Henderson <richard.henderson@linaro.org> wrote:

> If translation is disabled, the default memory type is Device, which
> requires alignment checking.  This is more optimally done early via
> the MemOp given to the TCG memory operation.
> 
> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> Reported-by: Idan Horowitz <idan.horowitz@gmail.com>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1204
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Hi Richard.

I noticed some tests I was running stopped booting with master.
(it's a fun and complex stack of QEMU + kvm on QEMU for vCPU Hotplug kernel work,
but this is the host booting)

EDK2 build from upstream as of somepoint last week.

Bisects to this patch.

 qemu-system-aarch64 -M virt,gic-version=3,virtualization=true -m 4g,maxmem=8G,slots=8 -cpu cortex-a76 -smp cpus=4,threads=2,clusters=2,sockets=1 \
 -kernel Image \
 -drive if=none,file=full.qcow2,format=qcow2,id=hd \
 -device ioh3420,id=root_port1 -device virtio-blk-pci,drive=hd \
 -netdev user,id=mynet,hostfwd=tcp::5555-:22 -device virtio-net-pci,netdev=mynet,id=bob \
 -nographic -no-reboot -append 'earlycon root=/dev/vda2 fsck.mode=skip tp_printk' \
 -monitor telnet:127.0.0.1:1235,server,nowait -bios QEMU_EFI.fd \
 -object memory-backend-ram,size=4G,id=mem0 \
 -numa node,nodeid=0,cpus=0-3,memdev=mem0

Symptoms: Nothing on console from edk2 which is built in debug mode so is normally very noisy.
          No sign of anything much happening at all :(

Jonathan



> ---
>  target/arm/tcg/hflags.c | 34 ++++++++++++++++++++++++++++++++--
>  1 file changed, 32 insertions(+), 2 deletions(-)
> 
> diff --git a/target/arm/tcg/hflags.c b/target/arm/tcg/hflags.c
> index 8e5d35d922..5da1b0fc1d 100644
> --- a/target/arm/tcg/hflags.c
> +++ b/target/arm/tcg/hflags.c
> @@ -26,6 +26,35 @@ static inline bool fgt_svc(CPUARMState *env, int el)
>          FIELD_EX64(env->cp15.fgt_exec[FGTREG_HFGITR], HFGITR_EL2, SVC_EL1);
>  }
>  
> +/* Return true if memory alignment should be enforced. */
> +static bool aprofile_require_alignment(CPUARMState *env, int el, uint64_t sctlr)
> +{
> +#ifdef CONFIG_USER_ONLY
> +    return false;
> +#else
> +    /* Check the alignment enable bit. */
> +    if (sctlr & SCTLR_A) {
> +        return true;
> +    }
> +
> +    /*
> +     * If translation is disabled, then the default memory type is
> +     * Device(-nGnRnE) instead of Normal, which requires that alignment
> +     * be enforced.  Since this affects all ram, it is most efficient
> +     * to handle this during translation.
> +     */
> +    if (sctlr & SCTLR_M) {
> +        /* Translation enabled: memory type in PTE via MAIR_ELx. */
> +        return false;
> +    }
> +    if (el < 2 && (arm_hcr_el2_eff(env) & (HCR_DC | HCR_VM))) {
> +        /* Stage 2 translation enabled: memory type in PTE. */
> +        return false;
> +    }
> +    return true;
> +#endif
> +}
> +
>  static CPUARMTBFlags rebuild_hflags_common(CPUARMState *env, int fp_el,
>                                             ARMMMUIdx mmu_idx,
>                                             CPUARMTBFlags flags)
> @@ -121,8 +150,9 @@ static CPUARMTBFlags rebuild_hflags_a32(CPUARMState *env, int fp_el,
>  {
>      CPUARMTBFlags flags = {};
>      int el = arm_current_el(env);
> +    uint64_t sctlr = arm_sctlr(env, el);
>  
> -    if (arm_sctlr(env, el) & SCTLR_A) {
> +    if (aprofile_require_alignment(env, el, sctlr)) {
>          DP_TBFLAG_ANY(flags, ALIGN_MEM, 1);
>      }
>  
> @@ -223,7 +253,7 @@ static CPUARMTBFlags rebuild_hflags_a64(CPUARMState *env, int el, int fp_el,
>  
>      sctlr = regime_sctlr(env, stage1);
>  
> -    if (sctlr & SCTLR_A) {
> +    if (aprofile_require_alignment(env, el, sctlr)) {
>          DP_TBFLAG_ANY(flags, ALIGN_MEM, 1);
>      }
>