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Thu, 25 Jun 2020 12:58:02 +0000 (UTC) Subject: Re: [RFC v5 12/12] pc-bios: s390x: Cleanup jump to ipl code To: Janosch Frank , qemu-devel@nongnu.org References: <20200624075226.92728-1-frankja@linux.ibm.com> <20200624075226.92728-13-frankja@linux.ibm.com> From: Thomas Huth Message-ID: <48329294-4c31-a1fa-20fb-ef6bb13e8550@redhat.com> Date: Thu, 25 Jun 2020 14:58:00 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20200624075226.92728-13-frankja@linux.ibm.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit 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 = 2020/06/25 02:30:11 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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 24/06/2020 09.52, Janosch Frank wrote: > jump_to_IPL_code takes a 64 bit address, masks it with the short psw > address mask and later branches to it using a full 64 bit register. > > * As the masking is not necessary, let's remove it > * Without the mask we can save the ipl address to a static 64 bit > function ptr as we later branch to it > * Let's also clean up the variable names and remove the now unneeded > ResetInfo > > Signed-off-by: Janosch Frank > --- > pc-bios/s390-ccw/jump2ipl.c | 27 +++++++++++---------------- > 1 file changed, 11 insertions(+), 16 deletions(-) > > diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c > index 767012bf0c..aef37cea76 100644 > --- a/pc-bios/s390-ccw/jump2ipl.c > +++ b/pc-bios/s390-ccw/jump2ipl.c > @@ -13,20 +13,15 @@ > #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; > +static void (*ipl_continue)(void); > +static uint64_t psw_save; I wonder whether there was a reason for having ipl_continue in the lowcore instead of using a simple static function pointer... Christian, do you remember? > static void jump_to_IPL_2(void) > { > - ResetInfo *current = 0; > + uint64_t *psw_current = 0; Mhh, what about using uint64_t *psw_current = (uint64_t *)lowcore instead, to make it more more explicit? > - void (*ipl)(void) = (void *) (uint64_t) current->ipl_continue; > - *current = save; > - ipl(); /* should not return */ > + *psw_current = psw_save; > + ipl_continue(); /* should not return */ > } > > void jump_to_IPL_code(uint64_t address) > @@ -46,15 +41,15 @@ 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; > + uint64_t *psw_current = 0; dito. > - save = *current; > + psw_save = *psw_current; > > - current->ipl_psw = (uint64_t) &jump_to_IPL_2; > - current->ipl_psw |= RESET_PSW_MASK; > - current->ipl_continue = address & PSW_MASK_SHORT_ADDR; > + *psw_current = (uint64_t) &jump_to_IPL_2; > + *psw_current |= RESET_PSW_MASK; > + ipl_continue = (void *)address; > > - debug_print_int("set IPL addr to", current->ipl_continue); > + debug_print_int("set IPL addr to", (uint64_t)ipl_continue); > > /* Ensure the guest output starts fresh */ > sclp_print("\n"); > The patch sounds like a good idea to me ... but since this code proofed to be very fragile in the past, let's wait for Christian to say whether there was a good reason for ipl_continue in the lowcore or not. Thomas