From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57847) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bVEDV-0006TP-G8 for qemu-devel@nongnu.org; Thu, 04 Aug 2016 04:41:26 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bVEDR-0000Mf-GN for qemu-devel@nongnu.org; Thu, 04 Aug 2016 04:41:25 -0400 References: <1470254107-14842-1-git-send-email-lvivier@redhat.com> <20160804023800.GE9189@voom.fritz.box> From: Laurent Vivier Message-ID: Date: Thu, 4 Aug 2016 10:41:16 +0200 MIME-Version: 1.0 In-Reply-To: <20160804023800.GE9189@voom.fritz.box> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] ppc64: fix compressed dump with pseries kernel List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson Cc: Alexander Graf , qemu-ppc@nongnu.org, qemu-devel@nongnu.org, Andrew Jones , Thomas Huth On 04/08/2016 04:38, David Gibson wrote: > On Wed, Aug 03, 2016 at 09:55:07PM +0200, Laurent Vivier wrote: >> If we don't provide the page size in target-ppc:cpu_get_dump_info(), >> the default one (TARGET_PAGE_SIZE, 4KB) is used to create >> the compressed dump. It works fine with Macintosh, but not with >> pseries as the kernel default page size is 64KB. >> >> Without this patch, if we generate a compressed dump in the QEMU monitor: >> >> (qemu) dump-guest-memory -z qemu.dump >> >> This dump cannot be read by crash: >> >> # crash vmlinux qemu.dump >> ... >> WARNING: cannot translate vmemmap kernel virtual addresses: >> commands requiring page structure contents will fail >> ... >> >> Signed-off-by: Laurent Vivier >> --- >> target-ppc/arch_dump.c | 5 +++++ >> 1 file changed, 5 insertions(+) > > Urgh.. so, really the page size used by the guest kernel is a > guest-side detail, and it's certainly possible to build a 4kiB page > guest kernel, although 64kiB is the norm. virtio-balloon doesn't work with 4K kernel. > This might be the best we can do, but it'd be nice if we could probe > or otherwise avoid relying on this assumption about the guest kernel. I agree with you but none of the other architectures probes for the page size. For instance ARM: |I cc: Drew to know how he has chosen the values] if (arm_feature(env, ARM_FEATURE_AARCH64)) { ... info->page_size = (1 << 16); ... } else { ... info->page_size = (1 << 12); ... } In the kernel: arch/arm64/include/asm/page.h: #define PAGE_SHIFT CONFIG_ARM64_PAGE_SHIFT arch/arm64/Kconfig: config ARM64_PAGE_SHIFT int default 16 if ARM64_64K_PAGES default 14 if ARM64_16K_PAGES default 12 choice prompt "Page size" default ARM64_4K_PAGES help Page size (translation granule) configuration. config ARM64_4K_PAGES bool "4KB" help This feature enables 4KB pages support. config ARM64_16K_PAGES bool "16KB" help The system will use 16KB pages support. AArch32 emulation requires applications compiled with 16K (or a multiple of 16K) aligned segments. config ARM64_64K_PAGES bool "64KB" help This feature enables 64KB pages support (4KB by default) allowing only two levels of page tables and faster TLB look-up. AArch32 emulation requires applications compiled with 64K aligned segments. endchoice I think we can't rely on the CPU state or the memory content as they can be corrupted. Thanks, Laurent