** Description changed: [ Impact ] * Linux 5.18 merged support for 5-level page tables (sv57), and it does it such that 5-level page tables are used whenever the system supports it. * So far only Qemu support sv57, but it breaks Go since Go uses too many of the upper bits of pointers to store data, and is not yet ready for sv57. It probably breaks other types of software - using too many bits for this "pointer tagging" technique. + using too many bits for this "pointer tagging" technique too. At the moment, there is no way to indicate to the kernel to downgrade to sv48, so we must patch the kernel: diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c index 2c4a64e97aec..18a0c70ed313 100644 --- a/arch/riscv/mm/init.c +++ b/arch/riscv/mm/init.c @@ -775,6 +775,10 @@ static __init void set_satp_mode(void) disable_pgtable_l4(); } + /* UBUNTU: Force disable sv57 and fallback to sv48 */ + if (pgtable_l5_enabled) + disable_pgtable_l5(); + memset(early_pg_dir, 0, PAGE_SIZE); memset(early_p4d, 0, PAGE_SIZE); memset(early_pud, 0, PAGE_SIZE); [ Test Plan ] * Build an image with the patched kernel and make sure snapd and - other Go programs works correctly and that you can compile a + other Go programs work correctly and that you can compile a simple helloworld written in Go. [ Where problems could occur ] * The patch could be buggy. * Qemu will no longer work with > 256 TB of memory.
-- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux-riscv in Ubuntu. https://bugs.launchpad.net/bugs/1991790 Title: Disable sv57 as the userspace is not ready Status in linux-riscv package in Ubuntu: New Bug description: [ Impact ] * Linux 5.18 merged support for 5-level page tables (sv57), and it does it such that 5-level page tables are used whenever the system supports it. * So far only Qemu support sv57, but it breaks Go since Go uses too many of the upper bits of pointers to store data, and is not yet ready for sv57. It probably breaks other types of software using too many bits for this "pointer tagging" technique too. At the moment, there is no way to indicate to the kernel to downgrade to sv48, so we must patch the kernel: diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c index 2c4a64e97aec..18a0c70ed313 100644 --- a/arch/riscv/mm/init.c +++ b/arch/riscv/mm/init.c @@ -775,6 +775,10 @@ static __init void set_satp_mode(void) disable_pgtable_l4(); } + /* UBUNTU: Force disable sv57 and fallback to sv48 */ + if (pgtable_l5_enabled) + disable_pgtable_l5(); + memset(early_pg_dir, 0, PAGE_SIZE); memset(early_p4d, 0, PAGE_SIZE); memset(early_pud, 0, PAGE_SIZE); [ Test Plan ] * Build an image with the patched kernel and make sure snapd and other Go programs work correctly and that you can compile a simple helloworld written in Go. [ Where problems could occur ] * The patch could be buggy. * Qemu will no longer work with > 256 TB of memory. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux-riscv/+bug/1991790/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
