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Thu, 27 Aug 2020 12:43:21 +0000 (UTC) Subject: Re: [PATCH v2 2/4] pc-bios: s390x: Use reset PSW if avaliable To: Janosch Frank , qemu-devel@nongnu.org References: <20200827093152.3026-1-frankja@linux.ibm.com> <20200827093152.3026-3-frankja@linux.ibm.com> From: Thomas Huth Message-ID: Date: Thu, 27 Aug 2020 14:43:20 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200827093152.3026-3-frankja@linux.ibm.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=thuth@redhat.com X-Mimecast-Spam-Score: 0.002 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US Received-SPF: pass client-ip=207.211.31.81; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/27 00:53:04 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -47 X-Spam_score: -4.8 X-Spam_bar: ---- X-Spam_report: (-4.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.959, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-1.782, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: borntraeger@de.ibm.com, cohuck@redhat.com, david@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 27/08/2020 11.31, Janosch Frank wrote: > If a blob provides a reset PSW then we should use it instead of > branching to the PSW address and using our own mask. > > Signed-off-by: Janosch Frank > --- > pc-bios/s390-ccw/bootmap.c | 1 + > pc-bios/s390-ccw/jump2ipl.c | 48 ++++++++++++++++++++++--------------- > pc-bios/s390-ccw/s390-ccw.h | 1 + > 3 files changed, 31 insertions(+), 19 deletions(-) > > diff --git a/pc-bios/s390-ccw/bootmap.c b/pc-bios/s390-ccw/bootmap.c > index 8747c4ea26..0df9b3781d 100644 > --- a/pc-bios/s390-ccw/bootmap.c > +++ b/pc-bios/s390-ccw/bootmap.c > @@ -515,6 +515,7 @@ static void zipl_run(ScsiBlockPtr *pte) > IPL_assert(entry->component_type == ZIPL_COMP_ENTRY_EXEC, "No EXEC entry"); > > /* should not return */ > + write_reset_psw(entry->compdat.load_psw); > jump_to_IPL_code(entry->compdat.load_psw & PSW_MASK_SHORT_ADDR); Shouldn't that be jump_to_IPL_code(0) now? Wouldn't it be cleaner to have a jump_to_IPL_PSW() function instead? > } > > diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c > index 767012bf0c..143d027bf7 100644 > --- a/pc-bios/s390-ccw/jump2ipl.c > +++ b/pc-bios/s390-ccw/jump2ipl.c > @@ -13,20 +13,28 @@ > #define KERN_IMAGE_START 0x010000UL > #define RESET_PSW_MASK (PSW_MASK_SHORTPSW | PSW_MASK_64) > > -typedef struct ResetInfo { > - uint64_t ipl_psw; > - uint32_t ipl_continue; > -} ResetInfo; > - > -static ResetInfo save; > +uint64_t *reset_psw = 0, save_psw, ipl_continue; I think the patch would be better readable if you'd split it in two - first the ResetInfo rework, then the use-reset-PSW-if-available stuff ? > static void jump_to_IPL_2(void) > { > - ResetInfo *current = 0; > + /* Restore reset PSW and io and external new PSWs */ > + *reset_psw = save_psw; The comment talks about io and external new PSWs ... but where is it in the code? > - void (*ipl)(void) = (void *) (uint64_t) current->ipl_continue; > - *current = save; > - ipl(); /* should not return */ > + /* No reset PSW, let's jump instead. */ > + if (ipl_continue) { > + void (*ipl)(void) = (void *) (uint64_t) ipl_continue; Is it possible to mark a function pointer with __attribute__((noreturn)) ? > + ipl(); > + } > + > + /* Reset PSW available, let's load it */ > + asm volatile ("lpsw 0(%0)\n" > + : : "a" (0):); I've never tried. but maybe you could add __attribute__((noreturn)) to an inline asm statement, too? > + /* should not return */ > +} > + > +void write_reset_psw(uint64_t psw) > +{ > + *reset_psw = psw; > } > > void jump_to_IPL_code(uint64_t address) > @@ -46,15 +54,12 @@ void jump_to_IPL_code(uint64_t address) > * content of non-BIOS memory after we loaded the guest, so we > * save the original content and restore it in jump_to_IPL_2. > */ > - ResetInfo *current = 0; > + save_psw = *reset_psw; > + *reset_psw = (uint64_t) &jump_to_IPL_2; > + *reset_psw |= RESET_PSW_MASK; > + ipl_continue = address; > > - save = *current; > - > - current->ipl_psw = (uint64_t) &jump_to_IPL_2; > - current->ipl_psw |= RESET_PSW_MASK; > - current->ipl_continue = address & PSW_MASK_SHORT_ADDR; > - > - debug_print_int("set IPL addr to", current->ipl_continue); > + debug_print_int("set IPL addr to", ipl_continue); > > /* Ensure the guest output starts fresh */ > sclp_print("\n"); > @@ -84,7 +89,12 @@ void jump_to_low_kernel(void) > > /* Trying to get PSW at zero address */ > if (*((uint64_t *)0) & RESET_PSW_MASK) { > - jump_to_IPL_code((*((uint64_t *)0)) & PSW_MASK_SHORT_ADDR); > + /* > + * Surely nobody will try running directly from lowcore, so > + * let's use 0 as an indication that we want to load the reset > + * psw at 0x0 and not jump to the entry. > + */ > + jump_to_IPL_code(0); > } > > /* No other option left, so use the Linux kernel start address */ > diff --git a/pc-bios/s390-ccw/s390-ccw.h b/pc-bios/s390-ccw/s390-ccw.h > index 36b884cced..7090720422 100644 > --- a/pc-bios/s390-ccw/s390-ccw.h > +++ b/pc-bios/s390-ccw/s390-ccw.h > @@ -78,6 +78,7 @@ int virtio_read(ulong sector, void *load_addr); > void zipl_load(void); > > /* jump2ipl.c */ > +void write_reset_psw(uint64_t psw); > void jump_to_IPL_code(uint64_t address); > void jump_to_low_kernel(void); > > Thomas