On 20/02/2024 17:50, Stefan O'Rear wrote: > On Tue, Feb 20, 2024, at 6:09 AM, Clément Léger wrote: >> Some userspace applications (OpenJDK for instance) uses the free MSBs >> in pointers to insert additional information for their own logic and >> need to get this information from somewhere. Currently they rely on >> parsing /proc/cpuinfo "mmu=svxx" string to obtain the current value of >> virtual address used bits [1]. Since this reflect the raw MMU mode >> supported, it might differ from the logical one used internally. >> Exporting the maximum mmappable address through hwprobe will allow a >> more stable interface to be used. For that purpose, add a new hwprobe >> key named RISCV_HWPROBE_MAX_KEY which will export the maximum mmappable >> userspace address. >> >> Link: >> https://github.com/openjdk/jdk/blob/master/src/hotspot/os_cpu/linux_riscv/vm_version_linux_riscv.cpp#L171 >> [1] >> Signed-off-by: Clément Léger <cleger@xxxxxxxxxxxx> > > Reviewed-by: Stefan O'Rear <sorear@xxxxxxxxxxxx> > > Ideally, we'd have something arch-independent, but this is a good interface > and simple enough to support in perpetuity. Hi Stefan, Indeed while not architecture specific, I did not found anything relevant in which this information could easily fit. sysconf is actually mainly compile time constants returned by the libc. And the few non POSIX sysconf defines (_SC_xx) are actually using either /proc parsing or the sysinfo syscall which did not changed since kernel 2.3. But maybe someone out there knows something better suited to export this information. Thanks, Clément > > -s > >> --- >> v2: >> - Note: tried sysconf to export it but this is not backed by syscall >> and thus does not allow exporting such information easily. >> - Use arch_get_mmap_end() instead of VA_BITS since it reflects the >> maximum logical address used by the riscv port >> - Change hwprobe key name from RISCV_HWPROBE_KEY_VA_BITS to >> RISCV_HWPROBE_KEY_MAX_ADDRESS >> - Link to v1: >> https://lore.kernel.org/lkml/20240201140319.360088-1-cleger@xxxxxxxxxxxx/ >> --- >> Documentation/arch/riscv/hwprobe.rst | 3 +++ >> arch/riscv/include/asm/hwprobe.h | 2 +- >> arch/riscv/include/uapi/asm/hwprobe.h | 1 + >> arch/riscv/kernel/sys_hwprobe.c | 4 ++++ >> 4 files changed, 9 insertions(+), 1 deletion(-) >> >> diff --git a/Documentation/arch/riscv/hwprobe.rst >> b/Documentation/arch/riscv/hwprobe.rst >> index b2bcc9eed9aa..a626aa21ac74 100644 >> --- a/Documentation/arch/riscv/hwprobe.rst >> +++ b/Documentation/arch/riscv/hwprobe.rst >> @@ -210,3 +210,6 @@ The following keys are defined: >> >> * :c:macro:`RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE`: An unsigned int which >> represents the size of the Zicboz block in bytes. >> + >> +* :c:macro:`RISCV_HWPROBE_KEY_MAX_USER_ADDRESS`: An unsigned long which >> + represent the maximum userspace mmappable address. >> diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h >> index 630507dff5ea..150a9877b0af 100644 >> --- a/arch/riscv/include/asm/hwprobe.h >> +++ b/arch/riscv/include/asm/hwprobe.h >> @@ -8,7 +8,7 @@ >> >> #include <uapi/asm/hwprobe.h> >> >> -#define RISCV_HWPROBE_MAX_KEY 6 >> +#define RISCV_HWPROBE_MAX_KEY 7 >> >> static inline bool riscv_hwprobe_key_is_valid(__s64 key) >> { >> diff --git a/arch/riscv/include/uapi/asm/hwprobe.h >> b/arch/riscv/include/uapi/asm/hwprobe.h >> index 9f2a8e3ff204..a6da434be9da 100644 >> --- a/arch/riscv/include/uapi/asm/hwprobe.h >> +++ b/arch/riscv/include/uapi/asm/hwprobe.h >> @@ -67,6 +67,7 @@ struct riscv_hwprobe { >> #define RISCV_HWPROBE_MISALIGNED_UNSUPPORTED (4 << 0) >> #define RISCV_HWPROBE_MISALIGNED_MASK (7 << 0) >> #define RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE 6 >> +#define RISCV_HWPROBE_KEY_MAX_USER_ADDRESS 7 >> /* Increase RISCV_HWPROBE_MAX_KEY when adding items. */ >> >> /* Flags */ >> diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c >> index a7c56b41efd2..19a47540b4a2 100644 >> --- a/arch/riscv/kernel/sys_hwprobe.c >> +++ b/arch/riscv/kernel/sys_hwprobe.c >> @@ -8,6 +8,7 @@ >> #include <asm/cacheflush.h> >> #include <asm/cpufeature.h> >> #include <asm/hwprobe.h> >> +#include <asm/processor.h> >> #include <asm/sbi.h> >> #include <asm/switch_to.h> >> #include <asm/uaccess.h> >> @@ -202,6 +203,9 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair, >> if (hwprobe_ext0_has(cpus, RISCV_HWPROBE_EXT_ZICBOZ)) >> pair->value = riscv_cboz_block_size; >> break; >> + case RISCV_HWPROBE_KEY_MAX_USER_ADDRESS: >> + pair->value = arch_get_mmap_end(ULONG_MAX, 0, 0); >> + break; >> >> /* >> * For forward compatibility, unknown keys don't fail the whole >> -- >> 2.43.0 >> >> >> _______________________________________________ >> linux-riscv mailing list >> linux-riscv@xxxxxxxxxxxxxxxxxxx >> http://lists.infradead.org/mailman/listinfo/linux-riscv
