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    SubjectRe: [PATCH 2/2] RAS: Introduce the FRU Memory Poison Manager
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    On 2/14/2024 6:05 AM, Borislav Petkov wrote:
    > On Tue, Feb 13, 2024 at 09:35:16PM -0600, Yazen Ghannam wrote:
    >> +static inline struct cper_fru_poison_desc *get_fpd(struct fru_rec *rec, u32 entry)
    >> +{
    >> + return &rec->entries[entry];
    >> +}
    >
    > This one needs to go too.
    >

    Ack.

    >> +static inline u32 get_fmp_len(struct fru_rec *rec)
    >> +{
    >> + return rec->sec_desc.section_length - sizeof(struct cper_section_descriptor);
    >> +}
    >
    > Oh well, I guess we can keep that one.
    >

    Okay.

    >> +/* Calculate a new checksum. */
    >> +static u32 get_fmp_checksum(struct fru_rec *rec)
    >> +{
    >> + struct cper_sec_fru_mem_poison *fmp = get_fmp(rec);
    >> + u32 len, checksum;
    >> +
    >> + len = get_fmp_len(rec);
    >> +
    >> + /* Get the current total. */
    >> + checksum = do_fmp_checksum(fmp, len);
    >> +
    >> + /* Subtract the current checksum from total. */
    >> + checksum -= fmp->checksum;
    >> +
    >> + /* Return the compliment value. */
    >> + return 0 - checksum;
    >> +}
    >
    > Let's get rid of that one.
    >
    > Also, I think it is called *complement* value and you simply do
    >

    Yep, good catch! (compliment)

    > /* Use the complement value. */
    > rec->fmp.checksum = -checksum;
    >
    > I'd say.
    >

    This was my first thought. Other checksum code in the kernel does
    the (0-X) thing. So I wasn't sure if there's any odd side effects
    of one over the other. And I didn't take the time to dig into it.

    > ---
    >
    > diff --git a/drivers/ras/amd/fmpm.c b/drivers/ras/amd/fmpm.c
    > index 9eaf892e35b9..f8799beddcc4 100644
    > --- a/drivers/ras/amd/fmpm.c
    > +++ b/drivers/ras/amd/fmpm.c
    > @@ -195,11 +195,12 @@ static u32 do_fmp_checksum(struct cper_sec_fru_mem_poison *fmp, u32 len)
    > return checksum;
    > }
    >
    > -/* Calculate a new checksum. */
    > -static u32 get_fmp_checksum(struct fru_rec *rec)

    I made this a helper because we need to validate the checksum when
    reading records from storage too.

    > +static int update_record_on_storage(struct fru_rec *rec)
    > {
    > u32 len, checksum;
    > + int ret;
    >
    > + /* Calculate a new checksum. */
    > len = get_fmp_len(rec);
    >
    > /* Get the current total. */
    > @@ -208,15 +209,8 @@ static u32 get_fmp_checksum(struct fru_rec *rec)
    > /* Subtract the current checksum from total. */
    > checksum -= rec->fmp.checksum;
    >
    > - /* Return the compliment value. */
    > - return 0 - checksum;
    > -}
    > -
    > -static int update_record_on_storage(struct fru_rec *rec)
    > -{
    > - int ret;
    > -
    > - rec->fmp.checksum = get_fmp_checksum(rec);
    > + /* Use the complement value. */
    > + rec->fmp.checksum = -checksum;
    >
    > pr_debug("Writing to storage");
    >
    >

    Thanks,
    Yazen

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