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X-Received-From: 2607:f8b0:4864:20::344 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-stable@nongnu.org, qemu-devel@nongnu.org, =?iso-8859-1?Q?C=E9dric?= Le Goater , qemu-ppc@nongnu.org, Anton Blanchard , linuxppc-dev@lists.ozlabs.org, David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Apr 14, 2020 at 09:11:31PM +1000, Nicholas Piggin wrote: > If mtmsr L=1 sets MSR[EE] while there is a maskable exception pending, > it does not cause an interrupt. This causes the test case to hang: > > https://lists.gnu.org/archive/html/qemu-ppc/2019-10/msg00826.html > > More recently, Linux reduced the occurance of operations (e.g., rfi) > which stop translation and allow pending interrupts to be processed. > This started causing hangs in Linux boot in long-running kernel tests, > running with '-d int' shows the decrementer stops firing despite DEC > wrapping and MSR[EE]=1. > > https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-April/208301.html > > The cause is the broken mtmsr L=1 behaviour, which is contrary to the > architecture. From Power ISA v3.0B, p.977, Move To Machine State Register, > Programming Note states: > > If MSR[EE]=0 and an External, Decrementer, or Performance Monitor > exception is pending, executing an mtmsrd instruction that sets > MSR[EE] to 1 will cause the interrupt to occur before the next > instruction is executed, if no higher priority exception exists > > Fix this by handling L=1 exactly the same way as L=0, modulo the MSR > bits altered. > > The confusion arises from L=0 being "context synchronizing" whereas L=1 > is "execution synchronizing", which is a weaker semantic. However this > is not a relaxation of the requirement that these exceptions cause > interrupts when MSR[EE]=1 (e.g., when mtmsr executes to completion as > TCG is doing here), rather it specifies how a pipelined processor can > have multiple instructions in flight where one may influence how another > behaves. > > Cc: qemu-stable@nongnu.org > Reported-by: Anton Blanchard > Reported-by: Nathan Chancellor > Tested-by: Nathan Chancellor > Signed-off-by: Nicholas Piggin > --- > Thanks very much to Nathan for reporting and testing it, I added his > Tested-by tag despite a more polished patch, as the the basics are > still the same (and still fixes his test case here). I did re-run the test with the updated version of your patch and it passed still so that tag can still stand without any controversy :) Thank you for the fix again! Nathan > This bug possibly goes back to early v2.04 / mtmsrd L=1 support around > 2007, and the code has been changed several times since then so may > require some backporting. > > 32-bit / mtmsr untested at the moment, I don't have an environment > handy. > > target/ppc/translate.c | 46 +++++++++++++++++++++++++----------------- > 1 file changed, 27 insertions(+), 19 deletions(-) > > diff --git a/target/ppc/translate.c b/target/ppc/translate.c > index b207fb5386..9959259dba 100644 > --- a/target/ppc/translate.c > +++ b/target/ppc/translate.c > @@ -4361,30 +4361,34 @@ static void gen_mtmsrd(DisasContext *ctx) > CHK_SV; > > #if !defined(CONFIG_USER_ONLY) > + if (tb_cflags(ctx->base.tb) & CF_USE_ICOUNT) { > + gen_io_start(); > + } > if (ctx->opcode & 0x00010000) { > - /* Special form that does not need any synchronisation */ > + /* L=1 form only updates EE and RI */ > TCGv t0 = tcg_temp_new(); > + TCGv t1 = tcg_temp_new(); > tcg_gen_andi_tl(t0, cpu_gpr[rS(ctx->opcode)], > (1 << MSR_RI) | (1 << MSR_EE)); > - tcg_gen_andi_tl(cpu_msr, cpu_msr, > + tcg_gen_andi_tl(t1, cpu_msr, > ~(target_ulong)((1 << MSR_RI) | (1 << MSR_EE))); > - tcg_gen_or_tl(cpu_msr, cpu_msr, t0); > + tcg_gen_or_tl(t1, t1, t0); > + > + gen_helper_store_msr(cpu_env, t1); > tcg_temp_free(t0); > + tcg_temp_free(t1); > + > } else { > /* > * XXX: we need to update nip before the store if we enter > * power saving mode, we will exit the loop directly from > * ppc_store_msr > */ > - if (tb_cflags(ctx->base.tb) & CF_USE_ICOUNT) { > - gen_io_start(); > - } > gen_update_nip(ctx, ctx->base.pc_next); > gen_helper_store_msr(cpu_env, cpu_gpr[rS(ctx->opcode)]); > - /* Must stop the translation as machine state (may have) changed */ > - /* Note that mtmsr is not always defined as context-synchronizing */ > - gen_stop_exception(ctx); > } > + /* Must stop the translation as machine state (may have) changed */ > + gen_stop_exception(ctx); > #endif /* !defined(CONFIG_USER_ONLY) */ > } > #endif /* defined(TARGET_PPC64) */ > @@ -4394,15 +4398,23 @@ static void gen_mtmsr(DisasContext *ctx) > CHK_SV; > > #if !defined(CONFIG_USER_ONLY) > - if (ctx->opcode & 0x00010000) { > - /* Special form that does not need any synchronisation */ > + if (tb_cflags(ctx->base.tb) & CF_USE_ICOUNT) { > + gen_io_start(); > + } > + if (ctx->opcode & 0x00010000) { > + /* L=1 form only updates EE and RI */ > TCGv t0 = tcg_temp_new(); > + TCGv t1 = tcg_temp_new(); > tcg_gen_andi_tl(t0, cpu_gpr[rS(ctx->opcode)], > (1 << MSR_RI) | (1 << MSR_EE)); > - tcg_gen_andi_tl(cpu_msr, cpu_msr, > + tcg_gen_andi_tl(t1, cpu_msr, > ~(target_ulong)((1 << MSR_RI) | (1 << MSR_EE))); > - tcg_gen_or_tl(cpu_msr, cpu_msr, t0); > + tcg_gen_or_tl(t1, t1, t0); > + > + gen_helper_store_msr(cpu_env, t1); > tcg_temp_free(t0); > + tcg_temp_free(t1); > + > } else { > TCGv msr = tcg_temp_new(); > > @@ -4411,9 +4423,6 @@ static void gen_mtmsr(DisasContext *ctx) > * power saving mode, we will exit the loop directly from > * ppc_store_msr > */ > - if (tb_cflags(ctx->base.tb) & CF_USE_ICOUNT) { > - gen_io_start(); > - } > gen_update_nip(ctx, ctx->base.pc_next); > #if defined(TARGET_PPC64) > tcg_gen_deposit_tl(msr, cpu_msr, cpu_gpr[rS(ctx->opcode)], 0, 32); > @@ -4422,10 +4431,9 @@ static void gen_mtmsr(DisasContext *ctx) > #endif > gen_helper_store_msr(cpu_env, msr); > tcg_temp_free(msr); > - /* Must stop the translation as machine state (may have) changed */ > - /* Note that mtmsr is not always defined as context-synchronizing */ > - gen_stop_exception(ctx); > } > + /* Must stop the translation as machine state (may have) changed */ > + gen_stop_exception(ctx); > #endif > } > > -- > 2.23.0 >