Re: [PATCH 16/19] EDAC, ghes: Fix grain calculation

Mauro Carvalho Chehab
2019-10-11T11:22:10Z

Em Thu, 10 Oct 2019 20:25:37 +0000
Robert Richter <rrichter@marvell.com> escreveu:

> The current code to convert a physical address mask to a grain
> (defined as granularity in bytes) is:
>
> e->grain = ~(mem_err->physical_addr_mask & ~PAGE_MASK);
>
> This is broken in several ways:
>
> 1) It calculates to wrong grain values. E.g., a physical address mask
> of ~0xfff should give a grain of 0x1000. Without considering
> PAGE_MASK, there is an off-by-one. Things are worse when also
> filtering it with ~PAGE_MASK. This will calculate to a grain with the
> upper bits set. In the example it even calculates to ~0.
>
> 2) The grain does not depend on and is unrelated to the kernel's
> page-size. The page-size only matters when unmapping memory in
> memory_failure(). Smaller grains are wrongly rounded up to the
> page-size, on architectures with a configurable page-size (e.g. arm64)
> this could round up to the even bigger page-size of the hypervisor.
>
> Fix this with:
>
> e->grain = ~mem_err->physical_addr_mask + 1;
>
> The grain_bits are defined as:
>
> grain = 1 << grain_bits;
>
> Change also the grain_bits calculation accordingly, it is the same
> formula as in edac_mc.c now and the code can be unified.
>
> The value in ->physical_addr_mask coming from firmware is assumed to
> be contiguous, but this is not sanity-checked. However, in case the
> mask is non-contiguous, a conversion to grain_bits effectively
> converts the grain bit mask to a power of 2 by rounding up.
>
> Suggested-by: James Morse <james.morse@arm.com>
> Signed-off-by: Robert Richter <rrichter@marvell.com>

Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

> ---
> drivers/edac/ghes_edac.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/edac/ghes_edac.c b/drivers/edac/ghes_edac.c
> index 851aad92e42d..97242cf18a88 100644
> --- a/drivers/edac/ghes_edac.c
> +++ b/drivers/edac/ghes_edac.c
> @@ -220,6 +220,7 @@ void ghes_edac_report_mem_error(int sev, struct cper_sec_mem_err *mem_err)
> /* Cleans the error report buffer */
> memset(e, 0, sizeof (*e));
> e->error_count = 1;
> + e->grain = 1;
> strcpy(e->label, "unknown label");
> e->msg = pvt->msg;
> e->other_detail = pvt->other_detail;
> @@ -315,7 +316,7 @@ void ghes_edac_report_mem_error(int sev, struct cper_sec_mem_err *mem_err)
>
> /* Error grain */
> if (mem_err->validation_bits & CPER_MEM_VALID_PA_MASK)
> - e->grain = ~(mem_err->physical_addr_mask & ~PAGE_MASK);
> + e->grain = ~mem_err->physical_addr_mask + 1;
>
> /* Memory error location, mapped on e->location */
> p = e->location;
> @@ -428,8 +429,13 @@ void ghes_edac_report_mem_error(int sev, struct cper_sec_mem_err *mem_err)
> if (p > pvt->other_detail)
> *(p - 1) = '\0';
>
> + /* Sanity-check driver-supplied grain value. */
> + if (WARN_ON_ONCE(!e->grain))
> + e->grain = 1;
> +
> + grain_bits = fls_long(e->grain - 1);
> +
> /* Generate the trace event */
> - grain_bits = fls_long(e->grain);
> snprintf(pvt->detail_location, sizeof(pvt->detail_location),
> "APEI location: %s %s", e->location, e->other_detail);
> trace_mc_event(e->type, e->msg, e->label, e->error_count,

Thanks,
Mauro