Re: [PATCH Part2 RFC v4 06/40] x86/sev: Add helper functions for RMPUPDATE and PSMASH instruction

[Peter Gonda]

> +int psmash(struct page *page)
> +{
> +       unsigned long spa = page_to_pfn(page) << PAGE_SHIFT;
> +       int ret;
> +
> +       if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
> +               return -ENXIO;
> +
> +       /* Retry if another processor is modifying the RMP entry. */
> +       do {
> +               /* Binutils version 2.36 supports the PSMASH mnemonic. */
> +               asm volatile(".byte 0xF3, 0x0F, 0x01, 0xFF"
> +                             : "=a"(ret)
> +                             : "a"(spa)
> +                             : "memory", "cc");
> +       } while (ret == FAIL_INUSE);

Should there be some retry limit here for safety? Or do we know that
we'll never be stuck in this loop? Ditto for the loop in rmpupdate.

> +
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(psmash);
>