| Message ID | 20221010112729.42522-1-emil.renner.berthing@canonical.com |
|---|---|
| State | New |
| Headers | show |
On 10/10/22 05:27, Emil Renner Berthing wrote: > [ 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. > 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 > simple helloworld written in Go. > > [ Where problems could occur ] > > * The patch could be buggy. > > * Qemu will no longer work with > 256 TB of memory. > > Alexandre Ghiti (1): > UBUNTU: SAUCE: riscv: mm: Force disable sv57 > > arch/riscv/mm/init.c | 4 ++++ > 1 file changed, 4 insertions(+) > Acked-by: Tim Gardner <tim.gardner@canonical.com>
Applied to unstable and kinetic. On Mon, 10 Oct 2022 at 13:49, Tim Gardner <tim.gardner@canonical.com> wrote: > > On 10/10/22 05:27, Emil Renner Berthing wrote: > > [ 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. > > 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 > > simple helloworld written in Go. > > > > [ Where problems could occur ] > > > > * The patch could be buggy. > > > > * Qemu will no longer work with > 256 TB of memory. > > > > Alexandre Ghiti (1): > > UBUNTU: SAUCE: riscv: mm: Force disable sv57 > > > > arch/riscv/mm/init.c | 4 ++++ > > 1 file changed, 4 insertions(+) > > > Acked-by: Tim Gardner <tim.gardner@canonical.com> > -- > ----------- > Tim Gardner > Canonical, Inc > > > -- > kernel-team mailing list > kernel-team@lists.ubuntu.com > https://lists.ubuntu.com/mailman/listinfo/kernel-team
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);