Re: [PATCH RFC v8 24/56] crypto: ccp: Handle the legacy TMR allocation when SNP is enabled

[Kalra, Ashish]

> > +static int snp_reclaim_pages(unsigned long paddr, unsigned int npages, bool locked)
> > +{
> > +	/* Cbit maybe set in the paddr */
>
> This is confusing.
>
> I suppose C-bit is treated as a attribute of PTE in the kernel not part of the
> PA. It means only a PTE might carry a C-bit.

snp_reclaim_pages() is also called for reclaiming guest memory, in which 
case the (guest) paddr will have the C-bit set. Hence this C-bit 
handling is done within snp_reclaim_pages() so that the callers don't 
need to handle it explicitly.


> The paddr is from __pa(page_address()). It is not extracted from a PTE. Thus, the
> return from them should never have a C-bit.
>
> BTW: Wouldn't it be better to have pfn as input param instead of paddr?
>
> The caller has struct page, calling snp_reclaim_pages(page_to_pfn(page), xxxxx)
> would be much clearer than the current conversion:
> page_address() (struct page is converted to VA), __pa() (VA is converted to PA)
> in the caller and then PA is converted to pfn here.
>
> > +	unsigned long pfn = __sme_clr(paddr) >> PAGE_SHIFT;
> > +	int ret, err, i, n = 0;
> > +
>
> should be unsigned int i, n; as the input param npage is unsigned int.
>
> > +	if (!pfn_valid(pfn)) {
> > +		pr_err("%s: Invalid PFN %lx\n", __func__, pfn);
> > +		return 0;
> > +	}
> > +
> > +	for (i = 0; i < npages; i++, pfn++, n++) {
> > +		paddr = pfn << PAGE_SHIFT;
> > +
> > +		if (locked)
> > +			ret = __sev_do_cmd_locked(SEV_CMD_SNP_PAGE_RECLAIM, &paddr, &err);
> > +		else
> > +			ret = sev_do_cmd(SEV_CMD_SNP_PAGE_RECLAIM, &paddr, &err);
> > +
> > +		if (ret)
> > +			goto cleanup;
> > +
> > +		ret = rmp_make_shared(pfn, PG_LEVEL_4K);
> > +		if (ret)
> > +			goto cleanup;
> > +	}
> > +
> > +	return 0;
> > +
> > +cleanup:
> > +	/*
> > +	 * If failed to reclaim the page then page is no longer safe to
> > +	 * be release back to the system, leak it.
> > +	 */
> > +	snp_mark_pages_offline(pfn, npages - n);
> > +	return ret;
> > +}
> > +
> > +static int rmp_mark_pages_firmware(unsigned long paddr, unsigned int npages, bool locked)
>
> The same comment as above. Better take pfn or page instead of paddr with
> redundant conversions.

Again, the paddr can point to guest memory so it can have C-bit set.

Thanks,
Ashish

> > +{
> > +	/* Cbit maybe set in the paddr */
> > +	unsigned long pfn = __sme_clr(paddr) >> PAGE_SHIFT;
> > +	int rc, n = 0, i;
> > +
> > +	for (i = 0; i < npages; i++, n++, pfn++) {
> > +		rc = rmp_make_private(pfn, 0, PG_LEVEL_4K, 0, true);
> > +		if (rc)
> > +			goto cleanup;
> > +	}
> > +
> > +	return 0;
> > +
> > +cleanup:
> > +	/*
> > +	 * Try unrolling the firmware state changes by
> > +	 * reclaiming the pages which were already changed to the
> > +	 * firmware state.
> > +	 */
> > +	snp_reclaim_pages(paddr, n, locked);
> > +
> > +	return rc;
> > +}
> > +